Well the thread has gone "off point" more than once with posts bringing up examples that don't quite fit the premise. Wasn't Xena a re-occuring guest-star rather than a supporting character? Fraiser was a one off character who goes from that to reoccuring to regular to his own spinoff. Sheldon as noted was always a lead in TBBT, who often has his own story in episodes. Howard seems to be more of a breakout, going from a supporting role to having entire episodes revolve around him. ( more so with the addition of Bernadette)
As for Mr. T and the A-Team, my memories of the show has dimmed, but I never got the impression BA was the central character/lead.