In literature, the competent man or competent woman is a stock character who can do anything perfectly, or at least exhibits a very wide range of abilities and knowledge, making him a form of polymath. While not the first to use such a character type, the heroes and heroines of Robert A. Heinlein's fiction are generally competent men/women (with Jubal Harshaw being a prime example), and one of Heinlein's characters Lazarus Long gives a good summary of requirements:
"A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects."
The competent man, more often than not, is written without explaining how he achieved his wide range of skills and abilities, especially as true expertise typically suggests practical experience instead of learning through books or formalized education alone. While not implausible with older or unusually long lived characters, when such characters are young it is often not adequately explained as to how they acquired so many skills at an early age. It would be easy for a reader to form the impression that the competent man is just basically a superior sort of human being.
Many non-superpowered comic book characters are written as hyper-competent characters due to the perception that they would simply be considered underpowered otherwise. Batman, for example, is typically depicted as a member of the Justice League of America alongside Superman, Wonder Woman, and Green Lantern, all of whom are superpowered whilst he lacks superhuman powers of any kind. As a result, despite his original depiction as a vigilante, modern depictions of Batman portray him as having achieved the peak-human possibility in all things physical and intellectual. The same treatment has been applied to Lex Luthor, who has always been Superman's archenemy despite the former's total lack of superhuman powers.
James Bolivar diGriz, aka The Stainless Steel Rat, hero of Harry Harrison's series of the same name. His wife Angelina and his sons James and Bolivar also qualify, as does his boss, Inskipp the Uncatchable, head of the Special Corps.
Jason dinAlt in Harry Harrison's Deathworld novels and stories.