A Case of the.... Prison Break - Episode 4-3

So can anybody answer this for me? Why does Dominic Purcell’s name appear first in the opening credits, when the show clearly centers around the character of Michael, played by Wentworth Miller? It’s clearly not an alphabetical thing, because “M” appears before “P.” And if it’s done by first name, well, that’s just ridiculous. I get that Dominic Purcell was better known when the show kicked off, but we’re not talking about Tom Cruise here. Does anybody know?

http://primetimepulse.com/2008/09/10/a-case-of-the-prison-break-episode-4-3/