Smith recently expressed his belief in a recent press interview that unpredictability is one of his Doctor's most important traits, reports The Mary Sue.
"I think he's always a loose cannon. I mean, the interesting thing is, we sort of pick up where we left him and he was on his own," the actor explained. "And as Amy says to him, he's got to be careful of travelling on his own. I think it makes him perhaps less compassionate somehow, I don't know."
Smith also teased that the departures of the Ponds (Karen Gillan and Arthur Darvill) will have a massive effect on The Doctor's psyche.
He explained: "What's really interesting about these next [few] episodes, which is the first season, if we tag that as the first season, it deals with the fall of the Ponds and the demise of those two great companions that the Doctor is hugely, hugely attached to and had such a significant impact on him as a character and for me as an actor.
"So that's bound to be an event that flips his universe massively."
Showrunner Steven Moffat recently teased that the return of Jenna-Louise Coleman as The Doctor's new companion at Christmas brings a new dynamic to the show.
Doctor Who continues this Saturday (September 8) on BBC One and BBC America with 'Dinosaurs on a Spaceship'.
Watch a trailer for 'Dinosaurs on a Spaceship' below: