Lois Lane is (of course) the Romantic Interest of Superman. She first appeared in Action Comics #1 (June, 1938), the first published Superman story. As such, she's the Trope Codifier for (a type of) superhero love interest- the one who doesn't realize that the hero she loves is also someone close to her. The characters inspired by her are countless.
Over the decades, Lois has been a symbol both for and against feminism; while she is a career woman (an Intrepid Reporter) who speaks her mind and goes for the big scoop regardless of danger, she has also been the object of mockery for not noticing that her fellow reporter Clark Kent is Superman. On this front she is normally joined by Clark Kent's other close friends, but she is closer to either of them than anyone else who does not know they are the same, and even in Lois and Clark where she does figure out the fact that Clark Kent is Superman before he tells her, she has made out with him on at least one occasion under both identities before that. She also gets marked down by some since she is constantly getting in trouble that she needs to be rescued from. However at least in some incarnations this often involves her as a bold, fearless attacker who will grad whatever large object is around and go after the local evil force, at times when such a force is in the process of defeating Superman without the use of Kryptonite.
During the Silver Age of comics, Lois had her own series, titled Superman's Girl Friend, Lois Lane. Which lasted for 137 issues, from March-April, 1958 to September-October, 1974. In this series, which had a more humorous tone, Lois became a shrew who constantly tried to prove that Clark was Superman on the assumption that he would *have* to marry her then. Instead of, you know, simply courting him the regular way. (Note that Superman himself was openly courting her, but Lois apparently felt that she still needed to prove herself smarter than him. No wonder she became a target of his Super Dickery so often. It should also be noted that this was how most superhero love interests flew anyway). To be fair, they DID truly love each other, both just had a lot of quirks to overcome.
Eventually, an adult version of the character of Lana Lang (originally created to serve the same role as Lois but in the Superboy series) also joined the cast, in order to force Superman into a Love Triangle (though Lana had pretty much the same personality as Lois, making you feel even sorrier for him.)
Other stories had Lois fall in relationships with other superheroes, including (in one Time Travel story) Superman's own father, Jor-El. Mostly she was just trying to make him jealous, or just happened to attract the attention of other Superman-like characters. Those stories always ended with Lois and Superman back in their original situation by the end, often because The Paolo turned out to be evil/a shape-shifting ameoba/from a planet with a toxic atmosphere/all of the above. Sometimes she became a superhero herself, also only briefly.
In some "imaginary" stories (meaning, not intended as part of the official canon) Lois did get to marry Superman, though almost always with bad consequences for her (having to hide from criminals, raising bratty superpowered kids, etc.) In one such story she married a (reformed) Lex Luthor instead!
By the 1970s, her series attempted to modernize: Lois no longer tried to rope Superman into a wedding, dressed less conservatively and the stories tackled more serious subjects. Unfortunately, one of them was racial injustice, which it tried to explore by... having Lois be transformed into a Black woman for one day. While the intention was good, the story felt very awkward, especially towards the end when she asked Superman if he would still love her if she never changed back.
Lois was eventually allowed to finally marry Superman; the first time, it was the original Lois Lane (the one from the 1940s comics) since that version was declared to exist in a Parallel Universe and was not the "current" version. Ironically, in this story Superman (due to a magic spell) forgets he's a superhero and marries Lois as Clark Kent. But then she discovers he's really Superman and helps him regain his memory. She expects him to declare the marriage null, but instead, he marries her again, this time as Superman (in a private ceremony.)
The modern Lois also got to marry Superman in the 1990s, first in the TV show Lois and Clark and then in the comics. This was the post-Crisis on Infinite Earths version, who was the 1970s version only more so. Most notably, her relationship (before she learnt his identity) was clearly with Clark, not Superman, in keeping with the Post-Crisis Superman's belief that "Superman is what I do, Clark Kent is who I am". There had been elements of this in the Bronze Age, but it was still mostly presented as "Lois is dating Clark because she suspects he's Superman". As of the New 52 reboot, Lois is no longer married to Clark, and is dating someone else.
Neither marriage had children, so far (except for her son in Superman Returns.) You also could count the adoption of Christopher Kent, a young Kryptonian boy who turned out to be the son of General Zod.)
Lois continues to be an inextricable part of the Superman mythos and appears in virtually every version of the character, be it comics, movies or animation.
- Action Girl: The modern version. She got smarter, too.
- Badass Damsel: She provides the page image. This is a woman who gets caught by villains all the frickin' time, but only because she's Genre Savvy enough to know that if she does so, she'll not only get the scoop on the front page story, but also somehow survive to write it. And not just by getting rescued — if Superman doesn't know/is depowered/is busy, she'll pretend to fall in love with the drug lord who captured her, then blast herself out of their wedding, veil, gown, and all, with a Mook's stolen machine gun.
- Even in the early days, Lois had quite the nerve. In some of the earliest Fleischer cartoons (now public domain) she pulls such stunts as trying to sabotage a getaway vehicle, climbing onto the back of a mechanical monster to see where it was going, blasting away with a submachine gun at would-be train robbers, and disguised herself as a Nazi to warn the American fleet of a U-boat threat(Well, it WAS the early forties).
- Betty and Veronica: To Superman, except she and Lana were both The Veronica. More recently, Lana's Betty and Lois is Veronica, when there's a question of it at all (for example, Smallville. These days, Lois is the Love Interest and Lana is the Unlucky Childhood Friend who has long since moved on.
- The Bus Came Back: Superboy's Love Interest Lana Lang
- Captain Ersatz: While Lois has been endlessly homaged and parodied, most people don't know that she herself was based off a 1930s movie character called Torchy.
- Characterization Marches On: Golden Age Lois was a lot more level-headed in early stories, occasionally getting herself out of trouble before Superman could do it.
- The Chick: Although she doesn't fit the role very well, Lois was reduced to this in many stories.
- Chuck Cunningham Syndrome: In the Golden Age comics, Lois had a young niece named Susie Thompkins, whose shtick was getting into trouble by telling fibs. Susie's last appearance was in the mid-50s; a few years later, Lois' (unmarried) sole sibling Lucy Lane was introduced, and Susie was never seen again, save a few appearances in the "Mr. and Mrs. Superman" stories of The Seventies. There, she's shown as the daughter of Earth-Two's married Lucy Lane Thompkins.
- Clingy Jealous Girl: Silver-Age Lois and Lana, though not Lori.
- Cosmic Plaything: As with Jimmy, some of the things Lois experienced happened because she was connected to Superman... and others just happened out of nowhere.
- Derailing Love Interests: If it is an Elseworld story, you can bet this is what happens to Lois, that is if she isn't just killed off.
- Friendly Enemy: Pre-Crisis, Lois and Lana were usually very good-natured about their love rivalry with each other.
- Henpecked Husband: What Superman becomes in some of the Imaginary Stories. And whilst the writing is misdirected, there is a tendency towards this in the recent canonical stories.
- Intrepid Reporter: Much more intrepid in the Modern Age, but to an extent in the old stories as well.
- Never Be a Hero: Unlike her fellow Superman supporting characters Jimmy Olsen and Lana Lang, Lois never had a superhero identity that was unique to her; other characters besides her have also been "Superwoman". (Jimmy has been 'Elastic Lad' and Lana was 'Insect Queen'.)
- Old Shame: The "I'm Curious- Black!" story was never referenced to again.
- Though it was included in at least one collection of classic Superman tales.
- Sealed Evil in a Can: Lois let these out quite often, in spite of repeatedly being told not to, even after all the other times she'd done it.
- Single Woman Seeks Good Man: Lois is in love with Clark not because he is Superman, but because he is a sweet, kind-hearted farmboy from Kansas.
- Transformation Comic: Often rivaled the Jimmy Olsen comics for this.
- Tsundere: The Trope Codifier.
- Weak-Willed: During the Golden Age she was very frequently (and easily) hypnotised. Oddly this was much more a trait of the Golden Age Lois who was assertive and had a very strong personality than the less feisty Silver Age version.
- Weirdness Magnet: As much as Jimmy Olsen. Heck, look at the Trope image, then know she's been aged prematurely, forced to marry a gorilla, and much, much more.
- What Could Have Been: Jerry Siegel intended to have Lois learn Superman's dual identity early on and get a Relationship Upgrade back in 1939 or so; as it happened, this did occur...in the mid-1990s