Wooster from the comics
Wooster is a fictional character created for the comic books based on the Mario video games. As a citizen of the Mushroom Kingdom, he is of the same species as other characters such as Toad, Toadsworth, and Toadette. However, like several other characters created for the comics, he does not appear in the games, though a letter column in one of the comic books alleges that he can be seen in the King's court in Super Mario Bros. 3. Wooster's role seems to be an advisor to King Toadstool, the father of Princess Peach. He does this job because the King is very dim-witted, and Wooster is often the one to make the decisions for him whether or not he likes it. He is, of course, well aware of King Toadstool's stupidity, to the point that he has written a list of people who say that the King is dumb (other Nintendo characters, among them). This could be seen as a passing nod to P.G. Wodehouse's Jeeves and Wooster stories, where Jeeves is the valet to the dim-witted Bertie Wooster.
Unlike most other Mario comic characters, Wooster's personality did not develop much, as he usually popped up to offer his comments on certain things. However, he was featured prominently in one particular story, "Betrayal Most Proper". In this story, King Toadstool buys himself a new crown, but Wooster does not like it, and calls it an abomination. The king is really angry at him for this and tries to force him to give "a humiliating apology and the whole affair will be forgotten" instead, so he resigns. Shortly afterward, he is captured by Bowser, and Mario and Toad go off to rescue him, despite King Toadstool forbidding them to do it, as he thinks Wooster has defected to Bowser's side. When Mario and Toad get to Bowser's castle, it seems as though Wooster really has switched sides, but it turns out he has fed Bowser enough junk food to induce hibernation.
Wooster was also a recurring character in the Nintendo Adventure Books.