Watching the most recent season of "Mad Men," it almost appeared as if actor Vincent Kartheiser was not aging well.

But you can't blame the 33-year-old actor for that. Instead, it's all Pete Campbell's fault.

Kartheiser recently told The Hollywood Reporter that he gained weight and even artificially created a receding hairline as part of the character development for his "Mad Men" character. It was a rough year, with Campbell fighting tooth and nail to establish his position as a partner in Cooper Sterling Draper Pryce, and even sleeping with a commuter buddy's wife.

Those things can take a toll on anyone, and Kartheiser said he wanted that to be reflected in Pete Campbell this season.

"I gained about 25 pounds -- none of it muscle," the actor said. "It was a very thin layer of hot huge sundae, chicken wings and pizza."

On top of that, Kartheiser had his hairline shaved back a quarter of an inch every couple of episodes.

"Later, when it grew back in, it looked completely ridiculous, like a five o'clock shadow," he said. "It's pretty wild to watch it -- my hairline looked crazy that last episode. It was surreal. I couldn't help but giggle."

"Mad Men" is certainly no stranger to changing characters' appearance to fit with storylines. January Jones, who plays a former model (and the former wife of Jon Hamm's Don Draper) gained a bunch of weight in what she initially thought may have been caused by an illness. Later, she is shown joining an early version of WeightWatchers.

Actress Elisabeth Moss, however, set the stage when she gradually gained weight over the course of the first season, which hid a surprise for the Season 1 finale.

"Pete's been in this place where he's not proud of himself for what he's done," Kartheiser said. "He's got a level of self-hate that these kinds of decisions really feed. It's bitterness seeping into his skin and infecting every molecule of his being. He's not Don Draper."