The attack was carried out for no apparent reason and left the popular longtime valet in critical condition.
"It was brutal," said A.J. Sacher, director of operations at the restaurant. "It really wasn't just an assault. It was attempted murder because after getting Frank unconscious through blows, he just stomped on his head."
It happened Sunday around 10 p.m. Witnesses say the shirtless suspect first attacked at least two other people out on the street.
Valet Efrain Zarazua, who went by Frank to co-workers, went out to see what was happening and the man suddenly turned on him.
He punched and kicked him repeatedly, with one final blow to the head.
"When I saw the footage, the way he beat him - it was terrible," said Frank's son Chris Zarazua. "Very terrible. He was defenseless, while this monster beat him almost to death."
The 51-year-old suffered a serious head injury and broken jaw.
He has worked as the valet at Barney's Beanery for more than 30 years.
His love of people and fancy cars have made him well-known among the restaurant's famous customers.
"It's a dreadful, and it's tragic," Sacher said. "It just makes you so angry. Frank, anybody who knows him, he's the best of us, and he was attacked by the worst."
A GoFundMe has been set up to help Zarazua.
"Once he sees this overwhelming support, he will see how much love he gets from everybody, and how much he is loved," said his son Chris.
Frank's family and friends say all they want is justice. The sheriff's department is investigating the series of attacks, searching for the violent suspect before he strikes again.
"It fills you with both sadness and anger because this person's still out on the street," Sacher said. "This person is still out there. Somebody like that is just looking for the next victim."