Does a character have to have its own detailled background or at least a definite personality and a name before it can be played? After one of my Saturday night gaming sessions, I mentioned that in the old days, the first D&D players sometimes/often didn't even name their characters until the third level or so. I've heard that Melf (of Melf's Minute Meteors, etc.) was so named because the player's character sheet said "M Elf" for male elf.* When I mentioned this little anecdote to one of my Saturday gamers, she did a thing that was awfully close to shuddering in horror.
I fancy myself a writer, and I often find myself building backgrounds and/or personalities for my characters. In a PbP game I'm playing in, I created a character and then thought, "Well, maybe he's from Ylarum." After doing a little research I found I didn't like that place as much as I thought I might, and eventually settled for the idea that the character is originally from Thyatis, though he's most recently been in Slagovich, and is now back in Specularum seeking adventure. I guess maybe he's gotten tired of spending weeks in the Sind desert looking for ancient artifacts.
But does it matter when you're first starting out? I shouldn't need to have a book in my back pocket with my character's background and homeland information and a flowchart of how he'll act in any given situation. I thought that was the actual original point of "role-playing": you assume a role, usually in the form of somebody who wants to go exploring something, and then you do what you think a person in that situation would do. As I understand it, in the old days the personality of the character was that of the player: the character was a tool the player used to experience what happened in the game; it was a pawn in the sense of a token on a gameboard. The character's background or race or class may have an effect on how it behaves in the game, but it doesn't need to step off the pages of a 200-page novel to be a valid character.
* I've since discovered that this anecdote is not literally true, but according to Melf's player, the character was named "Because Melf rhymes with elf and it's fun to say."