The character Thor, with Thor being his birthname I would guess, eventually "retires" as he loses his power to wield his hammer Mjolnir...and his arm. In the recent comics, it seems that a woman (not sure if she is identified somewhere) picks up the hammer and thus gains the power of Thor.
The following is an excerpt from wiki describing the incident:
Although Thor initially attempts to reclaim the hammer, after witnessing the woman wield its power against a Frost Giant invasion, he officially gives her the name and role of Thor, deciding to simply refer to himself as 'Odinson', using an artificial arm and Jarnbjorn as he continues to be a hero.
Fair enough that the woman gains Thor's powers and the hammer becomes hers but why on Earth (or indeed Asgard) was she given the name of Thor? Why not another name so that she is her own identity and hero instead of being given a name which would assume her to follow the footsteps and shadows of the previous male Thor?
I'm looking for any official sources, if one exists, that answers this or a similar question.