While almost every comic character who's existed for more than a year has an 'alternate self', Thor goes above and beyond in this sense. Due to shenanigans with his hammer Mjolnir, several other characters have taken up the mantle of Thor, notably Jane Foster, Eric Masterson, and Jake Olsen, to name but a few.
The reasons for these 'alternative' Thors range from reasonable to absolutely insane. For example, the paramedic Jake Olsen ends up being possessed by the spirit of Thor, who sort of takes over Jake for a while.
Given that this isn't the most bizarre event regarding who is Thor, it's pretty clear the dude's identity gets thrown around like a spirited game of dodgeball which, while exciting for us, has to be rough for the son of Odin.
The best part? These events also leave Thor responsible for a frog version of himself - affectionately known as Throg - because are you even a superhero if you haven't accidentally given a frog superpowers?