Donning blue face paint and a huge helmet, Ferrell took over the annual comic book exhibition in character.
But his gift of a box of doughnuts and a jug of orange juice clearly wasn't enough to go around.
He joked, "I didn't think there would be so many of you."
Ferrell's Megamind co-stars Tina Fey and Jonah Hill joined him for the first-day press conference, but another castmate, Brad Pitt, was only there in cardboard cut-out form.
The film's director, Tom McGrath, joked that Pitt "had to watch the kids" because his partner, Angelina Jolie, was also at Comic-Con.
Jolie, there to promote her new movie Salt, was the biggest draw of the opening day as thousands of film fans queued up for hours to see the star.