06/30/2008 AT 08:25 AM EDT
's maniacal twist on the Joker in The Dark Knight
in no way resembled his true character off set – that of a proud father to his 2-year-old daughter, Matilda, his costars say.
"Because he died people want a dark story [that] he was so obsessed with the character, he was so contaminated by the Joker and he couldn't sleep and all of that stuff," said costar Gary Oldman, who plays Lt. Jim Gordon in the film, adding that wasn't the case.
"In between takes he would sit on the curbside and smoke a cigarette and laugh and talk about his daughter Matilda," added Oldman Sunday at the press day for the film. "I thought he was just a beautiful kid. I thought he was just wonderful. I had a real affection for him.
Ledger, who died in January
, gushed about his daughter with actress Michelle Williams
to costars on set.
"Heath showed me pictures of [Matilda] ... [he] would come in and say she did this and she did that," recalled Aaron Eckhart, who plays District Attorney Harvey Dent in the sequel out July 18.
But Ledger's other love on set was for his character, the Joker. Eckhart added: "He really created his look. That character Heath loved so much. He really cared about the Joker."
Director Christopher Nolan said he needed an actor who would be "truly fearless" for the role and Ledger was up for the challenge.
"[For] those who knew him and those who had the privilege of working with him, it's pretty amazing the disparity between the person he was and the monster that he created for us," Nolan said. "To see that being created from this very gentle person is a real testament to his skill as an actor."