The story of how I became head admin is actually pretty boring. Moderators were needed, so I was made a global moderator. Then admins were needed, so I was made an admin. Then over time the other admins slowly lost interest and resigned until I was the only one left. I guess most of the people who were around here to see this have more-or-less left the community now. That's a bit sad.
It's not entirely clear, but for simplicity I usually say that I became head admin at the beginning of 2011, a little over a year after the forum was created.
The forum was originally located at bitcoin.org/smf, then forum.bitcoin.org (hence the redirect), and finally bitcointalk.org. Fun fact: The name "bitcointalk" was invented by Jeff Garzik, and he's the one who bought the domain.