Ozzie Guillen wasn't on the short list to replace Jerry Manuel after the 2003 season. However, Guillen managed to win over both owner Jerry Reinsdorf and GM Kenny Williams with an unorthodox job interview. The fact that Guillen was, ahem, unorthodox in his style probably is one of the main reasons he was hired, given that it is a rather appealing characteristic to both the owner and then-GM.
Unlike current manager Robin Ventura, his predecessor did have some relevant experience prior to being hired. In June 2001, the recently retired Guillen, joined former White Sox manager's Jeff Torborg's coaching staff in Montreal as third base coach following the firing of Felipe Alou. The next season, he followed Torborg, owner Jeffrey Loria and the rest of the Expos' infrastructure to the Marlins, after Loria acquired the team in a robber baron deal with MLB. Although Torborg was fired in mid-2003, Guillen stayed on with new manager Jack McKeon and won the World Series later that year.
It wasn't exactly the most impressive background but, when you're a White Sox, you're a White Sox for life in Reinsdorf's mind, and that was enough to push him over the top and into the manager's seat.
Guillen stuck around for almost eight seasons, orchestrating his own exit in late 2011 after his unorthodoxy had morphed into ennui. In between, he had what can only be described as a successful tenure, finishing with a 678-617 regular season record to go along with a 12-4 playoff record, fueled by an 11-1 barnstorm to the 2005 World Series win.
The 2005 AL Manager of the Year had only one truly horrid season, 2007, and the rest were either basically average or above. How much credit one can assign to a manager for overall win/loss records is a topic for another day - the GM/owner certainly have a larger say in it - but it's difficult to make the argument that Guillen was a very bad manager (at least when his heart was in it), though it's probably equally as difficult to argue that he was a very good one.
His handling of pitchers was largely excellent; pitching coach Don Cooper, the Judas to his self-portrayed Jesus, rightly deserves a lot of credit for that, too, but Guillen exhibited a basic and apparently intuitive understanding of it. His offensive philosophy, on the other hand, reflected the mid-1980s in which he matured as a slap-hitting, free-swinging, defense-first shortstop.
If bets had been taken on November 4, 2003, there wouldn't have been many who would have put money on Guillen lasting until almost the end of the 2011 season - not least because of his mouth. While that certainly reared its ugly head from time to time - perhaps most notably by calling kinda-sorta-writer-guy-who-yelled-on-TV Jay Mariotti a "fag" - the main contributing factor to his departure both in Chicago and in Miami was his on-the-bench performance and not his on-the-mike performance. And the latter is the only place where he's going to give his performances in the future.