Rovick died in his sleep at a nursing facility in Boise, Idaho, said his wife, Jacqueline.
A Toledo, Ohio, native who launched his broadcasting career in radio, Rovick was a newly hired staff announcer at KTTV-TV (Channel 11) when the Los Angeles station first went on the air in 1949.
In 1952, after KTTV acquired a batch of old cartoons and was searching for someone to host a daily cartoon show for children at 5:30 p.m., Rovick came up with a novel idea: Sheriff John.
Rovick knew longtime Los Angeles County Sheriff Gene Biscailuz, "and I had been an honorary Sheriff before I started the show because I was interested in law enforcement work," he told The Times in 2008.
So "I put on a khaki uniform and a badge and got a big white hat, sat at a desk and showed cartoons," Rovick recalled.
"Cartoon Time" with Sheriff John became an immediate hit with young viewers, earning an Emmy Award in 1953 for outstanding children's program.
KTTV by then had added a new show to its schedule at midday, "Sheriff John's Lunch Brigade," which stayed on the air until 1970.
"Come on now, laugh and be happy and the world will laugh with you," he'd sing in a smooth baritone, lip-synching as he entered the door of the sheriff's office set at the beginning of each show. The opening included leading his young viewers in reciting the Pledge of Allegiance.
"We talked a lot about safety, courtesy, manners and things like that," he told the Idaho Statesman in 2005. "We often had firemen or police officers as guests, and I'd warn the kids not to do things like play in the street or get into refrigerators or play with matches."
He'd also do occasional live remotes, taking viewers to see how bread was made, or how cars were assembled at a GM plant in Van Nuys. And, of course, he'd show cartoons (those with Crusader Rabbit were early favorites).
One highlight of the show, whose primary target was 4- and 5-year-olds, was Sheriff John's reading of the names of dozens of viewers who were celebrating birthdays. Then he'd sing "The Birthday Cake Polka" — "Put another candle on my birthday cake. We're gonna bake a birthday cake ..." — as a large cake revolved on a lazy Susan.
Sheriff John also had lunch along with his viewers — he'd usually eat a sandwich and have a glass of milk after saying a brief nondenominational prayer.
"It was a real good little prayer," he recalled in 2008 in The Times, the words still fresh in his mind: "Heavenly father, great and good. We thank thee for our daily food. Bless us even as we pray. Guide and keep us through this day."
Rovick acknowledged that it would be hard to get permission to say grace on a contemporary TV show.
"Oh, they'd fight me tooth and nail today," he said, but at the time no one complained.
"Isn't that amazing?" he said. "That was when everyone was trying to prove that God was dead, and I was out to prove he was still alive, and I won."
From the start, Rovick received encouraging mail from parents, who extended their gratitude for his lessons in manners, safety and patriotism.
"The kids always came first," he said in the 2005 interview. "To some of them, I was a father figure. That was the best thing about being Sheriff John. A lot of those kids loved me."