Maybe he was a lousy captain off the pitch but I think that's common among captains. It should be the managers duty to lead them off the pitch in the first place, anyway in my opinion.
Players of his standard are often incredibly ambitious and often times insatiable because they're never happy with what they have, they always want more success, to be bigger and better.
Vieira was the same, complete tool off the pitch, one of the most inspirational leaders the premiership has ever seen off it.
Zidane was a coaches nightmare because he never took orders from anybody but himself, yet was one of the greatest players and leaders of all time.
I think it's too much to ask for a driven, ambitious, dominating leader on the pitch to be a friendly, reasonable fellow off it.