Crews responded to the 8500 block of Lookout Mountain Avenue around 4:40 p.m. A total of 45 firefighters extinguished the blaze in about 33 minutes, according to the Los Angeles Fire Department.
Firefighters found a man dead inside the home. Officials have not released the man's name, but neighbors identified him as Will Rothschild of the powerful banking family.
A cause of death will be determined by the L.A. County Medical Examiner. It's unclear what may have started the fire, and the incident remains under investigation.
No other injuries were reported.
Rothschild was described by neighbors as an eccentric millionaire - or even billionaire - with multiple properties and dozens of expensive cars.
On a street lined with multi-million-dollar homes and mansions, occupied by celebrities and the powerful, Rothschild was said to have lived as a bit of a recluse.
While some neighbors had never seen him and assumed the house was vacant, those who knew him were saddened by the loss.
"It is very sad," neighbor Jim Moore said. "He was a good guy. A good neighbor."