Cannell died Thursday evening of complications associated with melanoma at his home in Pasadena, his family said.
In a career that began in the late 1960s when he sold his first TV script and took off as he soon became the hottest young writer on the Universal lot, Cannell created or co-created more than 40 TV shows, including "Baa Baa Black Sheep," "Baretta," "The Greatest American Hero" and "21 Jump Street."
Cannell, who formed his own independent production company in 1979, wrote more than 450 TV episodes and produced or executive-produced more than 1,500 episodes.
"He was one of the masters of good, old-fashioned generic television," said Robert Thompson, a professor of television and popular culture at Syracuse University and author of the 1990 book "Adventures on Prime Time: The Television Programs of Stephen J. Cannell."
"He did detective shows, he did adventure- dramas, he did fantasies," Thompson said. "He wasn't one of these guys who did, like, 'The Sopranos.' He was a meat-and-potatoes producer, writer and creator of television shows. And he did meat and potatoes really, really well."
"'The Rockford Files," the 1974-80 detective series co-created by Roy Huggins and starring James Garner, "was kind of a standard, formulaic detective genre show, but it was brilliantly executed. And Cannell could write state-of-the-art dialogue like few others of his time," Thompson said.
In 1978, he shared an Emmy Award for outstanding drama series for "The Rockford Files."
From writing "this really great dialogue" on "The Rockford Files," Thompson said, "he'd go on to form his company and do a show like 'The A Team,' this kind of goofy, fantasy Lone Ranger-like program. But once again, in Cannell's hands, it became a huge hit. It was delightfully funny to watch."
David Chase, who wrote and produced for "The Rockford Files" and later created "The Sopranos," recalled Friday that Cannell's characters displayed "weaknesses — they were fallible human beings. That was the beginning of viewers seeing a TV protagonist as someone like themselves."
Early on, Cannell developed a reputation for being extraordinarily prolific.
Indeed, in the spring of 1986, he had six hourlong shows on in primetime: "The A-Team," "Hunter," "Stingray," "Riptide," "The Last Precinct" on NBC and "Hardcastle & McCormick" on ABC.
Former NBC executive Warren Littlefield said the Cannell touch gave NBC a huge boost in the '80s.
"He understood what I'd call the vitamins and minerals of what the audience needed," Littlefield told The Times on Friday. "The daily grind of life can be so difficult for lots of people, and his shows would let you forget all that for an hour and just enjoy the thrill of the adventure."
Veteran producer Steven Bochco, who had been friends and colleagues with Cannell since the early '70s, recalled that every young writer on the Universal lot would stop by Cannell's office to read scripts from "The Rockford Files."
"They were so smart and so funny, and he was just knocking them out one after the other," Bochco told The Times on Friday. "He was not a cookie-cutter writer — he was completely original."
Saying Cannell had "boundless imagination" and was a master craftsman "who always did his homework," Bochco added: "As gifted and talented as he was, we all loved him because he was just one of the dearest people alive."
Since his first novel, "The Plan," was published in 1995, Cannell wrote 15 other novels, including the Shane Scully crime series.
Cannell's prolific output as a writer came despite having dyslexia, a reading disorder that caused him to flunk three grades before he finished high school.
He told the Birmingham News in 2004 that he didn't know he had dyslexia until he was in his mid-30s when he took one of his daughters to have her tested for dyslexia.
"For me, it was, 'OK, now I get it, now I understand,'" he said. "But I think it's been helpful to my whole writing process.
"It has absolutely freed me up from that curse of trying to be brilliant because it's really deepened my psyche. I don't take myself very seriously because of my early learning problems."
Cannell, who was born Feb. 5, 1941, in Los Angeles, always loved writing and dreamed of becoming a novelist as a teenager — even when he was flunking English in high school.
A turning point came for him in the early '60s when his creative writing teacher at the University of Oregon took him aside.
"He said, 'Look, it doesn't matter at all to me whether you can spell or not. As long as I can read it, that's all I require," Cannell recalled in a 1999 interview with the Dayton Daily News. "The feedback I got was so encouraging.
"After I left college — I did graduate despite my problems — he said, 'You should never quit this,' and I took him at his word."
While driving a truck for his father's successful home-decorating business, Cannell began writing TV scripts at night and on the weekends.
A script he sold for "Adam-12" led to a job as story editor on the series. After "Adam-12," he continued working on numerous series at Universal.
"I went through this period where I was the new genius," Cannell recalled in a 1997 interview with The Times. "I mean people were carrying me around the lot on a litter. I actually heard the words 'Stephen Cannell' and 'brilliant' used in the same sentence.
"When you've been the stupidest kid in class, that's a pretty appealing thing to hear."
He is survived by Marcia, his wife of 46 years; his children, Tawnia McKiernan, Chelsea and Cody; a sister, Lyn Neel; and three grandchildren.
Correspondent T. L. Stanley contributed to this report.