The actor plays ad agency boss Roger Sterling in the 1960s-based drama, and had to have his face darkened with make-up for a potentially controversial scene at a party, at which his politically incorrect character sand a song about slavery.
He admits he was reluctant to go through with it due to the historic implications of white men portraying African-Americans on screen, but agreed to shoot the scene after a discussion with his co-star Jon Hamm.
Slattery tells Britain's Culture magazine, "(Director) Matt (Weiner) told me last year, 'There's a sort of party at the beginning, and I'm gonna have Roger sing My Old Kentucky Home in black face.' I was, 'Oh, terrific.' It wasn't until I got in the car on the way home that I said, 'What the hell did he just say? Black face?'
"When I first read that script, I thought, 'I don't wanna do this, I really don't wanna do this'. So I called Jon Hamm and I said, 'Would you do this?' And he said, 'Do you mean, would I do it, or would I (as character Don Draper) do it?' So I thought, 'I don't really have any choice'.
"You sign for the character, and he's the logical messenger for that. You can't do some of the things my character has done and then decide you don't want to do that one."