Abe McDaniel, a 95-year-old World War II veteran, died after becoming trapped by the flames. Fire officials determined that an accidental electrical problem caused the blaze.
The fire broke out shortly after midnight at a duplex on the 100 block of Carlton Avenue.
The victim's neighbors, who live in an adjoining back unit, called 911 after their smoke detector went off. By the time firefighters arrived, the front unit was engulfed and the victim was dead.
"They were overcome by smoke in trying to attempt the rescue," said Pasadena Fire Department spokeswoman Lisa Derderian. "Upon arrival, we had heavy flames coming from the duplex. They alerted us that there was somebody trapped inside, made a very aggressive fire attack."
Firefighters contained the fire within 25 minutes.
The 53-year-old woman and her 17-year-old son who lived in the back unit survived.
McDaniel was described by his family members as active and closely involved with the community. He had lived in the unit since 1970, according to fire officials on scene.
Raquel Andrade, the victim's next-door neighbor, tried to douse the blaze with a garden hose before firefighters arrived.
"It's sad. I mean, Mr. Mac was a close neighbor. He always came down for the holidays. He always picked out our peaches and made us jelly," said Andrade. "It's just sad knowing that such a great man lived there and now he's gone."
The fatal fire is the first in Pasadena in about a year's time.
The coroner will determine the cause of death.
Derderian said the fire caused an estimated $30,000 in damage.
