One-Punch Man/Characters

Saitama

Just a hero for fun... And profit

The titular character, a hero who can defeat any threat with just ONE PUUUUUUUUUUUUUUUUUUUUUUUUUUUNCH!

Tropes exhibited by Saitama include:

Badass Abnormal After 3 years of his "intense training regiment", he has become the most powerful being in the universe it seems.
Badass Normal Even before he underwent his training regiment for 3 years, he managed to kill a monster crab guy with only a tie.
Badass Nickname It's the title of the series. Although, nobody calls him that IN the series itself.
Brilliant But Lazy His powers could be used for SO much, but he lacks the motivation to bother.
Calling Your Attacks All he does usually is punch someone, but occasionally he will do a move he calls "Consecutive Normal Punches." which is just him punching rapidly, OR in the rarest of cases, he does a punch from what he calls his "Serious Series".
Comically Invincible Hero Hence the name.
Complete Monster It's very funny and ironic to think that the monsters of the world that do battle with him, consider him this. It got to where he lives in an area of City Z alone with nobody else, be they person OR monster that is willing to live nearby him, with the exception of Genos.
Danger Deadpan According to him, he finds himself feeling less and less emotion due to how over-powered he has become. Thanks to his joining the Hero Organization and taking Genos as an apprentice, he seems to be a bit better.
Deadpan Snarker He is SO extremely powerful that he is almost constantly bored. He's also defeated countless super powerful bad guys and monsters, so he acts like he's heard just about every evil villain speech you can think of before.
Expy With his powers, he's like a bald Chuck Norris!
Heroic Sacrifice He practically DESTROYS his own hero reputation for the sake of other heroes and the organization as a whole's own reputation with the public.
Humble Hero: While the theme song suggests this is the case, Saitama did actively seek recognition. However when given the chance to receive credit for his actions, he threw it away so other heroes that risked their lives either to defeat a powerful foe or merely stall said foe from killing innocents till someone (or a group) who could defeat him arrived got recognition for their heroism.
Kryptonite Is Everywhere Somewhat literally. The only thing close that he has to a weakness is that he has a poor sense of directions which leads him to showing up at the last second. Well that, and he's kind of lazy.
Nice Guy He doesn't do his heroic deeds for admiration or glory. He does it because he wants to, and he never passes up a chance to help someone in need... So long as he hears about it.
Nightmare Fuel Anyone able to actually sense his power is terrified of him, except they also don't believe it when they see him, so they almost always underestimate him, which leads to them being punched.
Reason You Suck Speech He tends to just flatly tell his opponents to stop being evil or stop causing trouble. If they don't... They get PUNCHED! Some try delivering them TO him, but he tends to brush them off.
Too Awesome to Use His powers seem to have no limit, and the things he does regularly demonstrate that. However, if he were to use the full extent of his powers which NOBODY else knows haphazardly, the damage he could inflict could very well destroy the world and then some. THANK GOD, he seems to have extremely good control over it though, except that even if he holds back he still manages to stop any threat with a single punch.
Unskilled But Strong AND HOW!? He doesn't bother with trying to learn more advanced fighting techniques or strategies, because he's so powerful that he doesn't need to. His attack AND defense are portrayed as flawless. In fact, the only area of skill he seems to have outside of his powers is his mastered control of them. He knows how to hold back AND unleash his powers as he deems necessary in any given situation. Except that even some of his weakest uses are more than enough to turn his opponents into paste.
What the Hell Are You? His enemies and even his friends wonder how the hell he has his unstoppable power. If he's some sort of demon or deity or something.
What the Hell Hero Some people try to paint him as a fraud who steals credit for heroic deeds from other heroes. He later pretends to do exactly that during the Deep Sea King incident, because he wanted to avoid the populous losing faith in the organization as a whole, and so that the other heroes who fought wouldn't have lost public favor as well.
Worthy Opponent Yes, there's nobody who has ACTUALLY been a threat to him personally, but he still compliments some of the foes he faces... Right before he obliterates them with a single punch. Such as Lord Boros who was the first opponent we've seen to get him to use a move from his "Serious Series" of punch moves.

GENOS

The Cyborg Prince

A cyborg who lost his family when a crazy cyborg massacred his home town. He later meets Saitama and becomes both his apprentice and roommate.

Tropes exhibited by Genos include:

Ascended Fanboy Of sorts, he was immediately in awe of Saitama's unlimited power, so he asked to become his apprentice, and eventually convinces Saitama to let him become his roommate. While living together, Genos is almost constantly taking everything Saitama says as though it were Gospel, and studies his actions even him lounging about watching TV as though it were some sort of secret badass training regiment.
Heroic Sacrifice He pulls this at least twice. First was during his initial appearance while fighting Mosquito girl, he gets badly damaged and was unable to win, so he was about to self-destruct until Saitama stepped in. Then, during the fight with the Deep Sea King, he was doing pretty well at first, since technically speaking his powers DID have the capacity to weaken the DSK, but then a little girl yelled out how she believed he could win, which drew the attention and wrath of the DSK who spat a wad of acid at her. Genos was forced to throw his own body in front of it and take the hit which melts much of his body and leaves him (and everyone else) at the DSK's mercy. Had it not been for Mumen Rider and then Saitama's arrival, everyone present would have died.
Nice Guy Initially he was just fighting bad guys to test his powers, but his time with Saitama has helped him become a better person and hero.
No Kill Like Overkill When he spars with Saitama, he claims to be unleashing max output of his powers, and he wanted Saitama to do the same. Saitama then fakes him out and unleashes a single punch, but stops himself before touching Genos. The force of said punch obliterated the wall of the canyon they were standing in as well as parted some of the clouds in the sky. Leading Genos to realize he could never hope to reach the same amount of power Saitama has... No one could.
Oh Crap His moments of this generally come from him being so impressed by Saitama's limitless powers.
Pyromaniac His attacks and armaments all focus on unleashing intense flames.
Reason You Suck Speech He tries to dish out one or two, but they tend to backfire.
Too Dumb To Live Initially, he is very reckless when charging into combat. He usually underestimated his opponents or gets distracted which led to his defeat several times.
What an Idiot! Despite having some of the best weaponry and technology in the world comprising his body, he still has many instances where he underestimates his opponents and gets beaten because of it. He also tends to be so wrapped up in how powerful Saitama is, that he considers everything he says or does as though it were Gospel.

Mumen Rider

Cyclist for Justice!

The Top Ranked C-Class hero!

Tropes exhibited by this character include:

Badass Biker He rides an everyday normal bicycle, and yet is definitely a badass.
Badass Creed See Determined Defeatist below.
Badass Normal He's the highest ranked C-class hero, but it isn't because he has superpowers or abilities. It's because he does more heroic deeds than any other hero in class C, if not the world! Apart from Saitama, and even then he (Saitama) tends to go after the bigger threats he hears about.
Determined Defeatist: He holds no illusions of where he stands. But he tries anyways.

Mumen Rider: No one expects much ...from me. They think a C class won't be much help. I know that better than anyone! I'm not good enough for Class B. I'm weak. I know that much. No one has to tell me I have no chance of beating you. I already... know that!
Sea king: What are you babbling about? Begging for your life?
Mumen Rider: And yet, I must try. It's not about winning or losing. It's about me taking you on right here, right now!

Determinator In a world of super heroes with abilities that can do almost anything, HE is as far as we know, just an average man riding a bicycle. However, that doesn't stop him from working harder than probably any other hero out there, and yet he knows he isn't powerful enough to move up to any rank beyond C. Not that that matters to him anyway, because if there is ever a crisis, while other heroes may shrink away from danger, he always pedals straight for it. Why? Because that's what being a true hero is all about!
Foil To almost, if not ALL other heroes of the series, because so many of them are caught up in their rankings, fame, powers, and wealth to remember that they're supposed to be heroes always doing the right thing. He's even a foil to Saitama, because while they both have the right mindset as heroes, Saitama has seemingly limitless power whereas Mumen Rider is just an average human being.
Humble Hero He's an average man on a bike. He has no super powers beyond his determination, courage, and will. He knows that. He knows that because of that, people don't expect much from him. He knows that it would be pointless to try and rise up in ranks since he doesn't have the powers to handle said threats that those ranks regularly take on. And yet, he works hard and never stops trying to fight and do heroic deeds, be them small or big.
Pet The Dog After the Deep Sea King incident, many people were misled to thinking Saitama was a fraud that was stealing the credit from the other heroes who fought, including Mumen Rider. Some even sent him letters condemning him, but then he found one letter that thanked him for what he did. That one was from none other than Mumen Rider.
Reasonable Authority Figure Despite being the top ranked C-class hero, he doesn't flaunt his status or title over others. Unlike many other heroes both above and beneath him.
Reason You Suck Speech He delivers one... to himself... Sort of. It doubles as a Crowning Moment of Awesome as well as a Crowning Moment of Heartwarming and even a little bit of a Tear Jerker all at once!
Too Dumb To Live Yeah, him rushing into battles even when he knows he has no chance of winning is brave, but it's also very reckless. That said, in the case of him fighting the Deep Sea King who had already taken down several heroes of ranks both lower AND higher than him. Had Mumen Rider not fought, Genos as well as most if not ALL the civilians and other beaten heroes in the area would have been killed by the time Saitama arrived on the scene to finish the job.
Weak but Skilled He can certainly ride a bike better than anyone... That we know of.