Wildest character concept?
Like the favourite/recurring NPC post, I could just throw you Action Bastard again. This is actually a difficult question to ask, especially for someone with a good couple of decades of roleplaying under their belt. You get deadened to playing things like a community of weird singing, tree people, a demon violinist, or a dishonourably discharged space soldier/ex-gynaecologist who had hooks for hands.
As someone who always ends up being the GM, when I’m a player I often end up being a leader. I’ve made a good run of unreliable characters who ensure that this isn’t the case or punish the group for trusting them too much. My first proper one was Father Talwin, for a D&D Troupe game during Third Edition which ended up with me running full time for a while. He’s probably not the wildest, as that’s likely to belong to a one-shot RPG at some point, but he’s one of the weirder, more convoluted characters.
Talwin wasn’t just a multiclassed cleric/thief. He was formerly a cultist who’d guaranteed himself long life by sacrificing his loved ones. He went through a good thousand years acquiring new families and sacrificing them. A couple of times he went cold turkey and tried not to do this, but the lure of immortality was too much. A couple of family members got away, so there was an elf general ex-wife somewhere hunting him down and a daughter who was a seeded in as an informant for the group when I was running, so that if she and Talwin met, blood would be shed.
The thing is, you make a level one (or in this case two) character when you start. You don’t make Aragorn, you make Frodo. So Talwin sounded like he’d done a lot and was great, in an evil kind of way. He’d actually given up for good, sealed off his powers and become a cleric. The thing is, all the deeds he’d done drove him to drink. A lot. Also gamble. He lost his church to a stablehand in a game of pick-up sticks and started living underneath the group’s cart. Any money he earned as a cleric ended up going on booze, until he’d sobered up by being with them for a while. After that point, he started saving his money in order to build a new temple. While the group were purchasing magic items with their ill-gotten gains, Talwin’s plan was to build a temple to Kivarra, his deity. Also a casino, bar and grill, which would be attached to it.
Talwin was useless, spending a lot of time in or under the cart, hiding from problems, but he was good fun.