Captain Sweatpants frequents a comic book shop near you. Despite his mild-mannered appearance, he has all the answers about comic books...
...and life, if you can understand an answer given in the form of an analogy to a major DC or Marvel story arc.

Captain Sweatpants first appeared in The Hofstadter Isotope episode of the CBS hit series The Big Bang Theory. CBS has pulled the YouTube video, but the above is a picture of Captain Sweatpants. The dialog that introduced him on the series follows the unauthorized clip below.
Penny (about Stewart): "Ooooh! He seems like a nice guy!"
Leonard: "You mean for someone who's into comic books?"
Penny: "No! No, no, I just meant for... Yeah."
Leonard: "Penny, just because people appreciate comic books doesn't make them weirdos! Stewart's a terrific artist. He went to the Rhode Island School of Design."
Penny (pointing at Captain Sweatpants): "Okay, what about the guy over there in the superhero t-shirt tucked into his sweatpants?"
Leonard: "Ah, yeah, that's Captain Sweatpants. He doesn't really help the point I'm trying to make."
Captain Sweatpants appears browsing comics in the background at the start of the above clip from The Hofstadter Isotope.
He also appears browsing comics in the background at the very start of The Classified Materials Turbulance episode.
Captain Sweatpants is referenced at the start of this video, which occurs later in The Hofstadter Isotope. The dialog follows.
Penny: "Come on! I think it's nice that Captain Sweatpants showed up at your art opening!"
Stewart: "Yeah. It would have been nicer if he hadn't touched all the cheese!"
Captain Sweatpants appeared again in The Creepy Candy Coating Corollary.

Captain Sweatpants is portrayed by actor Ian Scott Rudolph.

The following news was received from Captain Sweatpants actor Ian Scott Rudolph in late March: