One-Punch Man

A 2009 webcomic about a bald guy.

Saitama is just a hero doing his hero job. The thing is, things are easy. Very easy. And that's because Saitama is powerful. Very powerful. To be more exact, almost 99% of his enemies go down in one punch. One. Punch. That's all thanks to Saitama's training, that apparently also made him bald. Thing is, Saitama has become so powerful and his job has become so easy, that he is becoming bored of the superhero business. Such a pity, because now is when both heroes and superpowerful monsters are finally noticing his existence.

The truth is, One-Punch Man isn't a serious story. It's a comedy and a parody of both superhero comics and fighting manga.

Written and self-published by ONE. A remake of the series, drawn by Yusuke Murata (of Eyeshield 21 fame) debuted in 2012, bringing an incredible art upgrade; this latter version was the one from where the character design for the 2015 anime adaptation came from.

Tropes used in One-Punch Man include:

All a Part of the Job: Saitama losing his hair, he feels is all part of the job. "Train hard everyday until your hair falls out."
All According to Plan: The central premise: Saitama wanted to become a super hero, and he got everything he wanted... Except that he became too strong and has begun to lose touch with his humanity.
All Aliens Have Superpowers: All monsters and aliens introduced seem to have some form of power beyond a normal human.
Ass Pull: The words of wisdom Saitama says to Genos. He does say some wise things, but he's secretly just making it up on the spot.
Ass in Ambassador: Saitama always tries to convince his foes to stop or surrender, but if and when they don't listen, they get punched.
Asshole Victim: The villains don't tend to get much development for us to feel the least bit sorry for them when Saitama punches them.
All There in the Manual: Saitama tells people the exact way he apparently got his powers, but no one ever believes him.
Badass: Many characters like Genos and Tornado are incredibly powerful and cool; in terms of power they are still little flies compared to Saitama.
Badass Normal: Several of the heroes are seemingly normal human beings, such as Mumen Rider, Tank-Top Tiger, and even the S-Class hero Metal Knight, who is actually just a seemingly normal human with high intelligence, but the bodies seen by the public are all robotic drones he sends out.
The Beast Master: Mosquito Girl can controls so much mosquitoes that her insect swarm is a very serious threat by itself.
Calling All Heroes: The Hero's Association works by recruiting heroes of all sorts into their ranks in order to organize and dispatch them to deal with threats as they come up.
Calling Your Attacks: Everyone does it. Even Mumen Rider. Hell, even Saitama does it a couple times when he isn't using his most basic punch.
Did You Just Punch Out Cthulhu?: Saitama against... Well... Anybody.
Dumb Muscle: The giant brute in the chapter three of the webcomic. At one point, his brother told him that Saitama was on his shoulder, and the brute reflexively swats at his shoulder... the one with his brother on it.
Exactly What it Says on the Tin: One-Punch Man. He's a dude, and all his foes tend to die from a single punch. Which makes it that much more special (both to him and the reader) when someone actually survives more than one punch from him.
Exactly What I Meant to Say: Saitama's words of wisdom to Genos. He's actually making things up as he goes, though some of it is genuinely good/wise advice.
Everyone Calls Him "Barkeep": People tend to address heroes by their "hero names", such as "Tornado", "Metal Bat", "Metal Knight", "Tank Top Tiger", "Mumen Rider", and... "Caped Baldy".
Fanservice: Of both female and male variety, thanks to Saitama's clothes being as not resistant as him and Tornado's permanently exposed thighs.
Fanservice Costumes: One of the characters' "costume" is a prison uniform, which he sheds when he unleashes his full power and proceeds to fight nude.
Flat Joy: Saitama's expressions are this, especially early on.
For the Evulz: A lot of the villains have pretty much no back story or character development whatsoever, so their reasons for being evil and doing what they do tends to boil down to this. Justified though, because from a writing perspective, what's the point in developing a bunch of villains if they all end up dead from a single punch from the main character?
Good Is Not Nice: Plenty of the heroes in the Hero's Association are fairly mean to people, including their fellow heroes, even if they are of the same rank.
Heel Face Turn: After Saitama (and Genos) wipe out all of the forces of the house of Evolution, the leader and his cyborg gorilla gave up the evil science bit and just opened a food stand.
Infinity+1 Sword: Saitama's body and especially his fists. Any villain that shows up may be strong enough to give the other heroes trouble, but not Saitama.
Jump Scare: Saitama pulls one off on a moleman bad guy from the House of Evolution, seconds before he punched him.
Kick the Dog: The villains LOVE doing this to everyone and anyone, and usually for no reason whatsoever than For the Evulz.
Look Behind You!: Saitama gets into fights with many people who show off their power, fighting skill, and speed. Saitama dwarfs them all and pulls this off a lot. Even Genos has it happen, and he nearly crapped his pants when Saitama seemed like he was going to punch him at "Kill Force".
Made of Explodium: Subverted: things that Saitama punches (enemies included) seem to be made of this, but his punches are just that strong.
Mole Men: Appear in one of Saitama's dreams, where they're trying to destroy mankind for Earth's resources, saying that's a matter of survival and only one of the two species can survive with the resources Earth have.
No Sense of Direction: Saitama gets lost a lot it seems, hence why he ends up taking so long to respond to some of the catastrophes and monster attacks that happen.
One-Hit Kill: Saitama's defining trope, as described in the page introduction.
Peace Through Superior Firepower: Part of the logic behind some of the actions of the members of the Hero's Association. Metal Knight seems to believe in this, although he never quite seems too into the "peace" part.
Prophetic Dreams: Saitama dreams of creatures from the underground invading the surface, with the invaders finally giving Saitama the fight of his life and the one he always wanted. He then meets them almost immediately after, but sadly they aren't as strong as they are in his dream, and Saitama easily forces them to surrender.
Quick Draw: Genos' equipment transforms and fires pretty fast. When he trains with Saitama, he tries to do this a lot.
Rank Inflation: Saitama starts out as one of the lowest in the C-class heroes, but due to his capture of Sonic and destroying a giant meteor, he gets to near the top of the C-class ranks very quickly - to the point that some of the other heroes think he was cheating his way up the ranks and taking credit for the works of other higher ranked heroes, leading to them beginning to spread rumors and wrecking his reputation.
Rank Up: The Hero's Association uses a class and rank-based system which lets heroes move up the ranks by performing heroic deeds.
Readings Are Off the Scale: Whenever someone senses, witnesses, or tries to measure Saitama's power, it's always said to be limitless. His abilities even broke ALL records of the physical exam for entering the Hero's Association.
Something Something Leonard Bernstein: The theme song is mostly in Japanese but has a little English.
Terrorists Without a Cause: Many of the monsters or villains that appear in the series have little to no reason, much less something close to justification for all the pain and suffering they inflict on people.
Ungrateful Townsfolk: Played with. Two heroes manipulating a bunch of plebians into blaming him for the damages to their home lives is the primary example. See below. But this is the common norm for most to all citizens whom generally have no real care for heroes to start with. Case in point, even though it was purposeful on Saitama's part. A number of people he'd saved from the Sea King all sent him a bunch of hate mail calling him a fraud.
Veganism and Vegetarianism: Tanktop Vegetarian from One-Punch Man has an expository name.
Victim Blaming: Tank-Top Black Hole and his brother Tank-Top Tiger turned the citizens of City Z against Saitama after he got moved up the ranks for destroying the meteor (which also ended up damaging much of the city). They thought Saitama was cheating to move up the ranks, but he DID destroy the meteor. However, he felt being blamed for the meteor at all was stupid since it was the meteor that destroyed everything, not him, so if they had a problem, they should take it up with the damn meteor.
Won't Work On Me: Most attacks used on Saitama are too weak to cause him any damage.
World of Badass: To the point where there's an entire hero organization, and even it doesn't necessarily contain every hero of their world.
You Again: People seeing Saitama tend to forget him, until after they see him in action doing what they deem impossible.
You Can See the Explosion from Orbit: "Serious Punch"