The Sixth Doctor was played by Colin Baker (no relation to Tom) from 1984 to 1986. Although I haven't seen any of his episodes, I get the feeling amongst Whovians that this is an incarnation that many fans want to forget. The Sixth Doctor was full of contradictions and clashes. Some may scoff at the levity of his multi-colored clown suit, but it may have signalled his internal chaos. I probably shouldn't give him the pop psychiatry diagnosis of "manic-depressive," but it seems right from what I've learned: sometimes he was bombastic and witty; sometimes he was petulant and volatile.
A big chunk of the 1985 season was devoted to a long story arc called "The Trial of a Time Lord," in which the Doctor was put through some byzantine ordeals, later found out to be orchestrated by an enigmatic Time Lord known as the Valeyard... who himself may have been a far-future incarnation of the Doctor himself. It turns out that the series itself was on trial at this time, since its ratings were slipping.
"Planets come and go. Stars perish. Matter disperses, coalesces, forms into other patterns, other worlds. Nothing can be eternal."
The Sixth Doctor is a CAPRICORN. Some appropriate keywords that I found for this sign include authority, discipline, and ambition. One possible negative trait is fatalism, which seems to apply, too -- especially to that quote above. Nevertheless, Capricorns are also patient, practical, and good with humor. (This is still the heroic Doctor we're talking about, here!)
This sign's New Year's Resolution is to release fear. In some cases, it may be that all those personality swings, including the brash and sometimes abrasive extroversion, may spring from internal clashes that circle around fear. Good Capricorns are said to be trustworthy and respected, but that can come at a cost. The source that I got these resolutions from said that "So much gets bottled up that you tend to lose touch with your need for spontaneous expression. Remember these old, wise words: The only thing to fear is fear itself."
[See the introduction for more about sources and motivations for this series of posts.]