A character who fits the tone of the campaign, the play-style of the group, and the temperament of the player. They must be competent enough to be a benfit to the group and must have at least one area where they outshine any other party member. The must have a backstory deep enough to give the character motivation to adventure and integreated enough to keep them with the party, but not so deep in impede further development, or so integrated that their removal would destroy the party. They must hold some ideals in regard but must be pragmatic enough to take the long view for their accomplishment and be willing to take actions tagential to their goals. THey must have a scope of motivation broad enough for me to hook them and a personality simple enough for me to predict how they will react to certain situations. They cannot be evil.
That my perfect character, I've never played him, I've never seen him in play, but one day I might, and it will be glorious.