Experienced Protagonist

"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."

- Robert A. Heinlein

Most works have the protagonist be a Farm Boy, New Meat, an Ordinary High School Student or Rookie Red Ranger.

Well, This Is Not That Trope.

An Experienced Protagonist starts out the story already knowing what he's doing, whether through formal lessons or being Taught By Experience. He's done what he does for a while. He might be The Dreaded or Famed in Story or a Living Legend, or a mentor to a genuine newbie, or even a Retired Badass (or soon-to-be) doing One Last Job. Any account of his origins or early days will be shown in prequel Origins Episodes, flashbacks or discussed after the fact, if it is ever depicted onscreen at all.

Despite this, such a character is not necessarily exempt from Mid-Season Upgrades, progression, and seeking out a mentor of his own. Perhaps he was a big fish in a small pond and the Big Bad is an Outside Context Villain who exposes him to a higher form of war that what he already knows and can do is So Last Season against. Perhaps some reason is contrived for him to Restart At Level One despite the initial A Taste of Power. Whatever the case, "continuous learning" can be as much a truism for the well-established fictional character as it is in reality.

Anime and Manga

 * Himura Kenshin of Rurouni Kenshin is already a war veteran, legendary assassin known as "Battōsai", and one of Japan's best swordsmen at series start. A number of antagonists come after him specifically because of his past deeds.
 * Kousei Arima from Your Lie in April is a Famed in Story former Child Prodigy pianist who stopped playing two years ago after a breakdown following the trauma of his mother's death. Much of the early part of the series revolves around him regaining the will to play and how others in the scene react to his return.

Film

 * Dredd: The eponymous Judge is a veteran lawman who is tasked with evaluating newbie Anderson.
 * Bryan Mills from Taken has "a very particular set of skills; skills ... acquired over a very long career." The kidnappers of his daughter laugh off his attempt at getting them to let her go. They don't live to regret doing so.

Literature

 * Outside of his juvenile novels, Robert A. Heinlein strongly favored competent, experienced people for his heroes. Male or female, they were usually proficient in multiple fields of endeavor, experts in their specialties, and often well-versed in many other fields as well.

Video Games

 * Alpha Protocol: Four of the five default background choices for Mike Thorton have him with achievements and experience whether in the military, government service or as a globetrotting Freelancer that have drawn the attention of the eponymous agency. This experience is reflected in having higher base skill points right from chargen. The sole exception is "Recruit", but completing a run with that selected unlocks the Veteran background that takes this Up to Eleven with Mike being a member of a similar organization that sought Alpha Protocol out by himself. Accordingly, a Veteran Mike has even more starting points and some unique dialogue reflecting this greater experience.
 * Many Grand Theft Auto protagonists are current or former criminals.
 * The various player characters of the Halo series have been fighting the Covenant invasion - or, in the case of the Arbiter, fighting for them - for years to decades by the time of the first game they're playable in.
 * Commander Shepard of Mass Effect has already gone through The Spartan Way needed to become a N7 and experienced combat, including one of three incidents in which he or she played a prominent role, before the player takes control for the first time.
 * Martin Walker of Spec Ops: The Line starts as a captain in Delta Force. Not that it helps much against what's waiting for him and his in Dubai.
 * Kazuma Kiryu of the Yakuza series has already had a multi-year career as a gangster and renown as the "Dragon of Dojima" when the first game starts. Unfortunately, a 10-year stint in prison early on leaves him rusty and in need of regaining his strength.