Dr. Dick Solomon
(John Lithgow) - High Commander of the aliens. Played by Lithgow as a Large Ham, Dick is an Insufferable Genius when it comes to science and a Ted Baxter when it comes to everything else. He is in love with and married Mary Albright and Mary Albright alone whether she likes it or not. His Earth job is as a physics professor.
- Comically Missing the Point: Doesn't understand sarcasm or lying very well.
- An example would be when Mary compared his family to The Addams Family. Dick assumed she meant second president John Adams. When she states that wasn't what she meant, Dick thinks she meant John Quincy Adams and becomes enraged that she would compare his family to "that freakshow".
- Did I Just Say That Out Loud?: Once blurted out to his class that Earth would be destroyed by a meteor in 2015.
- I Can't Believe It's Not Heroin!: Got addicted to collecting stuffed animals called "Fuzzy Buddies". His friends and family staged an intervention when it reached the point that he had so many he was keeping them in the freezer.
- Professional Butt-Kisser: Admits he became High Commander by doing this.
- Sadist Teacher: While handing out a test to his class, he openly told them that none of them would be able to solve question four, which made up half the test.
- He's actually really bad at what he does. Tommy's pointed out that he's had the same students in his class for six years.
- And Mary witnessed his pathetic attempt at teaching a little girl to play hopscotch in the park, which resulted in the little girl running away while Dick hurled insults at her.
- He's actually really bad at what he does. Tommy's pointed out that he's had the same students in his class for six years.
- Single-Target Sexuality: A subversion. Mary is the only woman with whom Dick considers himself to be truly in love with, and spends the length of the entire show either with her or trying to get back together with her. But he's had other relationships, including a one-night stand with the mother of one of his students.
- Sitcom Arch Nemesis: Had five the only frequent one being Vincent Strudwick. The other frequent one being Tony Johnson. The other two were fellow alien Liam Neeson, and grumpy lunch lady Lucy.
- What Does He See In Her?: The other aliens hate Mary and don't understand what Dick's obsession with her is. As the series progressed their opinion of her as a person softened, but they still hated the idea of the two of them together.
(Kristen Johnston) - Security Officer and Dick's "sister". A Hot Amazon who didn't like being "The Woman" at first, but eventually discovered that being a six-foot-tall blonde bombshell has its advantages. Works as the Solomons' homemaker despite being a Lethal Chef.
- Action Girl
- Ax Crazy: Borders on this at times, such as when her role as the security officer would require having to kill someone deemed a threat to the mission. Her solution to stop an auditor from discovering they're aliens was to snap his neck, and then the necks of everyone they encounter on the way home.
- I Can't Believe It's Not Heroin!: Was once addicted to buying shoes. Tommy commented that she had more shoes "than Italy". It reached a point that she was sleeping on shoe boxes.
- I Have Boobs - You Must Obey!: Gradually learns how to use this
- I Want My Beloved to Be Happy: In the last two episodes she turns Don into an effective police officer and gives him a backbone before leaving Earth, because she couldn't stand the thought of him spending the rest of his life as a muffin making coward.
- Mama Bear: Has the potential to be one.
- Their First Time: People are shocked to learn that someone of Sally's looks only recently lost her virginity to someone like Don.
(Joseph Gordon-Levitt) - Information Officer and Dick's "son", who is Really Seven Hundred Years Old, but got stuck at Compulsory School Age. He was in High School for most of the series, but he eventually graduated and went to college, at which point he was more-or-less demoted to Recurring Character.
- Did Not Get the Girl: Actually, he did get the girl. But Sally misconstrued Alissa's thoughts on graduation to her wanting to break up with Tommy, so she told her that he was breaking up with her. He had two chances to get back with Alissa afterwards, and blew both of them. The first, Tommy wound up telling everyone at graduation in his valedictorian speech about how they made out on her parents bed. The second, he tried to sacrifice Alissa to save himself when it appeared that there was some maniac brandishing a power tool in Alissa's backyard. It was Sally and Harry pulling some hair-brained scheme to push the two back together again.
- Grumpy Old Man: Tommy's actually the oldest of the aliens, and quite pissed that he's in a young body subjected to raging hormones.
- Important Haircut: In season four he finally gets his hair cut. This is around the time Joseph Gorden-Levitt started to get older.
- Traumatic Haircut: Stated that he actually missed his longer hair.
- Only Sane Man: Among a quartet made up of a Ted Baxter, a Hot Amazon, and a Too Dumb to Live Kavorka Man.
- The Casanova: He's easily the oddest of the aliens, yet he has had the most relationships with gorgeous women who could easily do better than him.
- His romantic interests have included Vicki Dubcek, Nina, an alien played by Cindy Crawford, a body builder policewoman named Janice, and in the last episode we find out that for the entire show he'd secretly been with Mrs. Dubcek.
- Cloudcuckoolander: Worst of the four.
- Eyes Always Shut
- Flanderization: When the series began Harry was just as odd, only quiet and a little subtler. As the seasons went on he started becoming louder.
- Genius Ditz: He's not very bright in terms of book smarts, but he's the most artistically gifted and has surprisingly no trouble dating women way out of his league. He also cracked the bar code.
- I Want My Beloved to Be Happy: He told Vicki that she should stay with the Big Giant Head because he was sincerely trying to do right by her and Eric Travis, and he didn't want Dick to get punished for disobeying orders.
- Kavorka Man
- Likes Older Women: Has been with Mrs. Dubcek.
- Too Dumb to Live
Dr. Mary Albright-Solomon
(Jane Curtin) - Dick's (initially reluctant) Earthling love interest and sometimes later wife and an anthropology professor at his college. She is a neurotic Christmas Cake who was a Good Bad Girl in her younger days, a fact which Dick seemed to be oblivious of in earlier episodes.
- Broken Bird: Her alternate universe counterpart "Kiki" is this, a bitter and cold woman who doesn't believe in love anymore. Mary has the potential to be this, but she actually handles all of the stress of a horrible childhood and a somewhat crappy career better than you would expect.
Mary: Dick, I can't have children.
- Dude, Where's My Respect?: She found her thesis in the bottom of box labelled "Sugar Puffs".
- Dysfunctional Family: Her parents both had affairs while she was growing up (including one that draws doubt to Mary's paternity). She's the eldest of three children, all twisted in their own ways. Her brother Roy sells aluminum siding and tells women he was abducted by aliens as an attempt to get laid. Her sister Renata is an affected, wealthy woman who has a personal vendetta against Mary and does everything in her power to destroy Mary's life (including trying to steal Dick). Their whole family seems fond of alcohol, and Mary has apparently followed in her mother's footsteps to become a borderline Lady Drunk.
- First-Name Basis/Last-Name Basis: Dick initially calls her "Dr. Albright", but permanently switches to "Mary" after they hook up for real and they became engaged halfway in the series. The other aliens refer to her as just "Albright" before changes her last name to simply "Solomon" after she married Dick. Nina and Vicki call her "Dr. Albright" before changing her husband's last name to "Solomon" making the Solomons the only couple while the other professors call her "Mary".
- Hard-Drinking Party Girl: Borders on this. She's known at the local supermarket as the "White Zinfandel Lady".
- Actually came in handy, as this rendered her immune to the drugged wine given to her by Charlotte from "Alien Hunter". Of course, it didn't help when she knocked Mary out with the gnome.
- Hilariously Abusive Childhood: Well, maybe not "abusive", per se. Her parents were close to emotionally abusive, however, and this is played for laughs.
- Love Triangle: Managed to have not one, but two relationships with two different alien beings.
- My Beloved Smother: Her mom's a complete bitch.
- My God, What Have I Done?: Had this moment when she realized she had sex with Dick while locked in the school library, under intoxication. This was during one of their "engagement" periods.
- Not That Kind of Doctor: Not matter how many times Mary has to explain it, Vicki keeps thinking that the "doctor" in her name means Mary's a medical doctor.
- Ted Baxter: Once compared herself to Abraham Lincoln in a speech to her colleagues. And, in Nina's words, "he did not come out favorably".
- What Does She See in Him?: Her relationship with Dick.
(Ryan Gosling) - Mary's illegitimate teenage son and Tommy's lifelong best friend and later step-brother. A Street Smart A Only Sane Man whose Book Dumb kid gots some neurotic sense of humour after he had a more reconnection with him.
- Control Freak: Became one in the later episodes.
- Hair Flip: He had short blonde hair for most of its run, and later got a haircut in the final season, though.
- Heterosexual Life Partners: With Tommy.
- Relationship Upgrade: Kyle and August towards halfway through Season 2, but they broke up in Season 3 for good.
- Will They or Won't They?: Kyle and Alissa towards the beginning of Season 4, but they broke up in Season 6 however.
- Wacky Guy
Promoted To Opening Titles In Season Three
- Only Sane Man: Whenever dealing with Mary and Dick.
- Pet the Dog: Nina normally seems to hold Dick in contempt (not entirely without reason, it must be said), but there are some moments when she makes it clear that she doesn't actually hate him.
- Shipper on Deck: Sometimes she's portrayed as supporting the Dick/Mary ship, but other times she has a What Does She See in Him? attitude about their relationship.
- Sassy Secretary
- Sexy Secretary: One episode involved Rodney having romantic fantasies about Nina, which Dick is horrified after seeing them making love in front of Nina's desk.
- Will They or Won't They?: Nina and Rodney, they hook-up for real around the show's first six seasons in the series, After five years of being together they became engaged in the two-part series finale.
(Carl Anthony Payne II) - A more postal office worker, who is the object of Nina's affections also works as Dick and Mary's straight man. In most episodes spends most of the time having a Badbutt.
Officer Don Orville
(Wayne Knight) - A portly, dim-witted cop with an overblown image of himself as an enforcer of justice. Sally is likeminded in her desire for harsh discipline and finds him incredibly attractive. Don is clueless as to why such a gorgeous woman is interested in him, but is more than happy to go along with it.
Mrs. Mamie Dubcek
Dr. Judith Draper
(Ileen Getz) - A fellow professor known for her monotone and sarcasm.
- Annoying Laugh
- Conspiracy Theorist: One-time occurrence. Once thought the ladies room had a hidden camera and dismantled the ceiling tiles looking for it.
- Deadpan Snarker
- Imaginary Friend: Mary believes her boyfriend Trent is imaginary.
- Les Yay: Sends Mary flowers after Dick, dressed as a woman, french kisses Mary at a womens seminar. Judith states "I knew it all along".
- Noodle Incident: Entered Mary's office, and the respective episode, finishing a conversation with Mary that ended with her saying "and when they found him, he was completely devoured by woodland creatures."
- The Stoic.
Dr. Vincent Strudwick
- Characterization Marches On: As the show went on she gradually became more stuck-up and hypocritical, until she finally broke up with Tommy after she admitted that she was cheating on him.
- Deadpan Snarker
- Laser-Guided Karma: Following her break up with Tommy, when he became editor of the school paper he kept telling people that their break-up had left her a wreck and that HE broke up with her. She kept having to remind people to her frustration that the reverse happened, but no one listened.
- Pet the Dog: Wrote a rather scathing review of Alissa's performance in the high school play, but told Tommy (the editor of the school paper at the time) that she would understand if he didn't print it since Alissa was his girlfriend.
(Chris Hogan) - Bug's Heterosexual Life Partner.
(Jan Hooks) - The skanky white-trash daughter of Mrs. Dubcek and Harry's on-off girlfriend. She repeatedly fails to understand that Mary is Not That Kind of Doctor and has a Southern accent for some reason. Ultimately, she ended up being Queen of the Universe. Don't ask.
- Chewing the Scenery: Her conversations with Harry will usually begin to sound like they're in a porno. Their first sexual encounter happened on Thanksgiving, on Mrs. Dubcek's kitchen counter and involved Harry wearing a turkey carcass on his head.
- Large Ham: After she becomes the Big Giant Head's wife, but even then she had plenty of moments.
- Lovable Sex Maniac: Most of her personality, really.
- Psycho Ex-Girlfriend: Becomes one as a Compressed Vice in "The Big Giant Head Returns Again". She seems to get over Harry at the end of the episode, but it was her last appearance on the show anyway.
Big Giant Head
(William Shatner) - The aliens' Evil Overlord. The Ghost for most of the series, but he eventually showed up as an Adam Westing Shatner. On Earth, he goes by the alias "Stone Phillips", the name of an NBC reporter at the time of the show's run.
Dr. Liam Neesam
(John Cleese) - An evil alien way better than Dick who briefly worked at Dick's college as a biology professor.
- Everything's Better with Monkeys: In his second appearance, he came back to Earth with plans to turn everyone into monkeys in order to turn it into an amusement park, "Planet Monkey World". Dick winds up turning Liam into a chimpanzee in order to stop him. Unfortunately, Mary saw the whole thing, and this leads to Dick admitted he's an alien.
- Evil Is Petty: Was originally sent to blow up Earth. Why? We're blocking his home planet's view.
- Back to 3rd Rock from the Sun