how did he venture into acting?
As a stand-up comedian.
Craig T. Nelson
Nelson began his show business career as a stand-up comedian. 
when did the first disney incredibles come out 2004. who is the producer? Pixar Animation Studios. name the voice cast? Craig T. Nelson, Holly Hunter, Sarah Vowell, Spencer Fox, Jason Lee, Samuel L. Jackson, and Elizabeth Peña. was the movie based on a comic book? Yes. what was the name of the book? "The Incredibles" who is the first person under voice cast you mentioned in your answer? Craig Theodore Nelson is an American actor and former stand-up comedian.
wiki:20110090
Craig T. Nelson [SEP] Career
Nelson began his show business career as a stand-up comedian. He was an early member of The Groundlings comedy troupe. Nelson, Barry Levinson, and Rudy De Luca formed their own comedy team and were regular performers at The Comedy Store. In 1973, Nelson left the comedy world, explaining "the standup comedy life was pretty unfulfilling for me" and he settled in Montgomery Creek, California where there was no electricity and no running water; "it was contentment, "The Waltons"", he said. Nelson had different jobs during that time including janitor, plumber, carpenter, surveyor, and high school teacher. He returned to acting five years later.