Crash Nebula is a superhero from the TV show of the same name. Like the Crimson Chin, he is a comic/TV show within a TV show.
Much like the Crimson Chin, Crash Nebula is a fictional hero treated with much love and respect by Timmy and his friends. He is a parody of Harvey Birdman, Space Ghost, and The Flash. He is very muscular and attractive, Mrs. Turner and Vicky even define him as a "hunksicle".
He has his own television series.
In his first appearance, Timmy, Chester McBadbat, and A.J. were watching Crash Nebula in Timmy's bedroom. During the show, Crash Nebula attempts to save his comrades from aliens, but ends up as their prisoner as the episode ends.
In the episode of the same name, it is revealed that he comes from a normal family who live on a farm. One day while "doing his chores" (really just lazing about), a space station appears and a butterfly-like creature runs out being chased by buggish robots. He then saves her and it is revealed that she is the Princess Galexandra who owns and runs the best school in the galaxy. So he gets a free scholarship.
He says good-bye to his parents and his dad gives him the lucky family manure. So he goes to the school only to be laughed at. But he makes friends (who are also geeks). On his first day, by accident, he opens up a portal that goes directly into space. The portal then sucks in the most popular girl in school. So to save her, he goes into space with the space suit The Nebula 3000. But the power runs low. So in an attempt to save himself and her, he puts in his manure. The fuel automatically goes up and he saves the day. The girl then says "You idiot! You crashed the Nebula!" He then says "That's it!" thus his name, Crash Nebula!