The eponymous character in Voltaire's Candide. Unfortunately for him, the trope is invoked only to be totally deconstructed, since he doesn't live in the best of allpossible worlds.
Rincewind, except he pays more attention to the disasters than the luck in surviving them, and so thinks he is cursed by The Lady... which is why she loves him so much.
Colon and Nobby from the City Watch books have important clues and crimes fall into their laps by pure luck so often that it's the unofficial reason they're still on the force when it has otherwise moved on into a respectable organization.
Tim Powers wrote a pair of novels — Expiration Date and Earthquake Weather — which explicitly riff on this trope, and on the idea of characters being archetypically related to the Tarot generally.
Firebird (Lackey) inverts this, Ilya's only pretending to be a fool, and is in fact cursed with bad luck.
Gimpel The Fool, a man doomed to forever be trolled by everyone.
Hercule Poirot's friend Hastings has some elements of this. As a detective trying to solve the mystery with Poirot, he's an abject failure. However, he's very good at pointing out the "obvious" things that sometimes slip by Poirot's notice.
Hasting's best performance in this role comes in The ABC Murders: The other detectives are distressed at the "bad luck" that sent one of the anonymous letters astray, causing it to reach them too late to prevent the murder. Hastings points out that the letter could easily have been deliberately misaddressed in order to give the killer enough time.
Allan Karlsson, the title character of The Hundred-Year-Old Man Who Climbed Out the Window and Disappeared, changes the course of history an astounding number of times throughout his life, and avoids death just as often. Being badly educated and having no interest in politics, he's often dismissed as an idiot. This suits him well, because all he wants is a glass of good alcohol, a hot meal and a nice place to sit down.
Blake Thorburn in Pact embodies this trope, even having the Fool card drawn for him from the Major Arcana. Rather than be cautious and pragmatic, he acts impulsively and on instinct, which in a setting where most magicians that last are patient and cautious is usually unexpected for his enemies. This strategy gives him momentum, but Ultimately gets him defeated by a demon, who severs his connections to the world and turns him into an Other. Afterwards, he becomes more cautious, but retains his instincts-now he knows when to wait and when to strike.
A classical example would be Perceval, in the Grail poems of the middle ages, especially in Chrétien de Troyes' Perceval ou le Conte du Graal.
A subversion in the Realm of the Elderlings saga, in which the Fool knows precisely what he is doing.
In Tales of the Five Hundred Kingdoms, the Fool is a Traditional role who trades his dignity for a whole lot of blind luck. While some Fools are genuinely dim, really Genre Savvy souls can play the Fool, as Sasha does at his wise father's encouragement, and enjoy the same benefits.
Plenty of P. G. Wodehouse characters. Bertie Woosterhung a lampshade on it in Carry On, Jeeves: "Providence looks after all the chumps in this world, and personally, I'm all for it." (Though Bertie isn't as perfect an example as some of Wodehouse's protagonists.)
