It really depends on the game.

Arthur MacMillan got "constructed". I had an idea what I wanted, did the needed research and one piece fell into the other. Including his extended family and some strenghts and weeknesses. So the character got some background as setup and will develop from there.

In another game I just grabbed an archetype, changed the gender, part of the name and off to the races he went. That character developed very much during play over the next two years.