The Drupal Security Team was originally created in 2005. Though we handled security issues before that, we didn't have a team with proper infrastructure until then. At that time, Károly Négyesi (chx) was the team leader. In July 2006 chx changed his role in the team and I promoted Heine Deelstra to be the security team lead. Heine recently stepped down as the security team lead, and I'm pleased to announce that Greg Knaddison (or greggles on drupal.org) will be filling this role.
Greg has been a consistent member of the security team and both Heine Deelstra, the security team members, and myself unanimously agreed that Greg is the logical person to head the Drupal Security Team.