Mike Farrell, I mean. Any role I’ve seen him in, like MASH, or Providence, or his recent one-time appearance on L&O:SVU, he’s always played a nice guy.
Has he ever played a nasty sumbitch? and if not, is he truly a nice guy playing off his own personality, or in private does he kick puppies and play nice guys as a dramatic challenge?
According to IMDB, in “The Crooked E: The Unshredded Truth About Enron,” he played Kenneth Lay. 
He played a physically abusive husband in Battered. Battered (TV Movie 1978) - IMDb
I’ve met him a few times In Real Life and at one of the events he seemed quite peeved in conversation about lack of attendance when he was the guest speaker. But the other times he was very gracious. So maybe that time he was having a bad day.
In other words, I don’t know but I would guess that he is a Nice Guy in his private life as well as onscreen.
[spoiler]MF’s wife has vanished while on honeymoon. A woman appears, claiming to be his wife, but MF says she is an imposter. The policeman doesn’t take him seriously, and is sure that the woman really is his wife.
Turns out that MF murdered his wife for the insurance, and the impostor is an undercover cop who tricks him into incriminating himself. [/spoiler]