Dirk Drain-Head, "the World's First Two-Fisted Action Plumber", is a fictional superhero created for the Super Mario comic books published by Valiant Comics. He appears in his own comic book series within the stories, making him in a fiction-within-fiction character.

Dirk is Mario's favorite comic book star, and is first briefly mentioned in the story "A Mouser in the Houser". A fuller look at him is given in a later story, titled "The Adventures of Dirk Drain-Head". Dirk's origins are never explained, but what is known about him is that he uses "It's Plungin' Time!" as his catchphrase. Also, his comic book only seems to come out quarterly, yet has managed to have reached at least 658 issues.

Mario seems to have an obsession with this character, as he sometimes rants about how awesome Dirk is, and has even been known to spend three entire days of reading Dirk's comics. This greatly annoys the other good guys and cause them to think less of Mario for reading Dirk's adventures. Luigi and King Toadstool hate Dirk, and Princess Peach thinks he's silly. Peach, strangely, seems to have an obsession of her own with another comic book, Baroness Blue Blood, "the Cheerful Champion of Social Status", which she considers "the only magazine worth reading in our generation". The opinions of Toad and Wooster are unknown.

It is quite odd that Luigi would hate Dirk - the two characters look exactly alike. It is unknown if Luigi is aware of his resemblance to Dirk, but Mario has at least once noticed the similarities in appearance. Incidentally, according to Mario, "Dirk drives his brother crazy too!"

In spite of Mario seemingly being the only good guy to be a fan of Dirk, many enemies also love the character. Shy Guys, Ninjis, and Birdo are among them. Lemmy Koopa is also a big fan of Dirk. It is unknown whether or not Bowser is also a fan, but he has been known to buy Baroness Blue Blood comics to line his Birdo cages with.

In another story, "Bedtime for Drain-Head", Mario is shown to sometimes sleep-walk, thinking he is Dirk. As a result of this, he disappears for hours, usually looking for Dirk's teenage comedic sidekick, Snakey. Snakey apparently gets his superhero name from wearing a plumber's snake around his waist. As part of his costume, he has also been said to wear socks without shoes. It is unknown whether or not Snakey is Dirk's aforementioned brother, or if he greatly resembles Mario (to match Dirk's resemblance to Luigi).

In this same story, among the Dirk comic books Mario has collected, one particular cover features a villain called Dark Dirk. Judging from this name, the character mentioned is obviously an evil twin, and could also be considered the Dirk Drain-Head counterpart of Waluigi.

The last story to tell us more about Dirk is "The Revenge of Pipe Ooze!" Pipe Ooze is Dirk's archnemesis, who is apparently either a guy with slime all over him, or slime in general. Like several other comic book villains, Pipe Ooze has a sidekick - the also-slimy Muck. Also first mentioned in this story is Dirk's pal Rusty Water, who is apparently a rusted faucet.

The Pipe Maze hosts an annual Dirk Drain-Head convention with a role-playing game.