Captain Impressive is the superhero persona of Earl Sinclair. In the fourth season Dinosaurs episode "Earl, Don't Be a Hero," Earl leaps into a lake filled with toxic waste. When he resurfaces, he has a strange glow which brings out the color of his eyes. Though the glow fades, Earl discovers that he can fly through the air. Roy Hess uses his knowledge of comic books to surmise that Earl has gained a vast arsenal of superpowers: flight, heat vision, and the ability to guess the weight of anything within a single pound.
Roy explains that Earl must use his powers to fight for truth, justice, and the Pangaean way. In order to protect his family, and impress Baby Sinclair with a snazzy title, a superhero name is required. Thus, with the aid of an eye-mask and a tartan cape, Captain Impressive is born.
Since this origin story is unknown to the population at large, considerable speculation arises over the true past of Captain Impressive. Robbie Sinclair theorizes that the Captain was born on a distant planet to an intelligent race. Charlene Sinclair, however, has heard that he lives under the sea in a domed kingdom.
Captain Impressive captures criminals, saves the Earth, and rapidly replaces Captain Action Figure as Baby's favorite superhero. However, due to the casual use of his heat vision to toast Roy's sandwich, Earl's secret is revealed to B.P. Richfield. Richfield informs Earl that according to his employment contract, all activity and proceeds from supernatural powers obtained by employees are under the direct control of WESAYSO.
Captain Impressive is then reduced to a corporate puppet and becomes a wholly owned division of WESAYSO, appearing at mall openings and in commercials. Though the rest of the family critique the new Captain Impressive, Baby continues to idolize his hero. Richfield launches a new TV series, The Captain Impressive Action Fun Hour, which airs on the Dino-Shopping Network and serves to sell such questionable products as the Captain Impressive action figure/fish knife, Captain Impressive pajamas (made from newspapers) and the Captain Impressive trachea plug.
After Baby Sinclair calls to order the trachea plug, Earl finds the courage to take a stand, and reveals his true identity. After a good shower wipes off the toxic goo which gave him his power, Captain Impressive's career comes to an end. Earl loses his powers, but has a considerably improved body odor.