Colin Callender, former president of HBO and overseer of some 80 Emmys and two dozen Golden Globes, will officially leave HBO by the end of 2008 to start his own production company after 21 years with the pay cable outlet, according to several news reports.

While the entire industry has been gossiping for months about Callender’s departure, no one was quite sure who was responsible.

Callender told Men’s Vogue Magazine: “I’ll stay here at HBO as long as they’ll have me.” And he also told the New York Times yesterday that the decision “was entirely of my own making” and not related to any HBO house-cleaning dictum.

Two executives who have worked with Callender in overseeing the production of films and mini-series at HBO will now divvy up his duties. Kary Antholis will become president of HBO Miniseries and Len Amato will become president of HBO Films. They will report to programming group/West Coast operations president Michael Lombardo.

Callender was one of several longtime HBO executives whose names arose as potential replacements for Chris Albrecht, who left his post as chief executive of HBO in mid-2007.

But that job was split among four executives, sparking the rumors in Hollywood that Callender, among others, might leave HBO.

Callender also told the Times, “I’ve had this growing feeling over the last year or so that there are growing opportunities in the marketplace.”