Character/Personality Creation?

To keep a long-winded question relatively brief, I got to thinking about the various characters and their personality blurbs and appearances in the books, and wanted to know how all that stuff was decided. Were you given a list of sets from the designers that you then had to come up with character concepts for, or was it the other way around? Was coming up with them a group effort with the rest of the story team, or something the head had already decided, or was it down to you to do on your own? How much do you feel your own character preferences may or may not have influenced this process, such as with groups like the Piraka or Barraki, for example?