Ronald Poppo had a hard-knock life on the streets.

A homeless drinker who had been shot once and arrested two dozen times, he is fighting for his life at Jackson Memorial Hospital’s Ryder Trauma Center after an 18-minute cannibal attack that cost him most of his face. At 65, he’s been homeless for almost four decades.

His hardscrabble existence took a volatile turn Saturday afternoon, when he encountered Rudy Eugene, a 31-year-old former North Miami Beach High School football player who liked to smoke marijuana and hoped to start his own mobile car-wash business.

Eugene died in a hail of police bullets when he mauled Poppo in a sudden and unprovoked attack. Eugene will be forever remembered as the Miami Zombie.

“Rudy was not a face-eating zombie monster,” said his high school friend Victoria Forte. “The Rudy we know was a nice gentleman with a warm smile, and funny.”

It’s unclear what brought the two unlikely characters together on the MacArthur Causeway. Poppo was known for hanging out on and under the bridge there; Eugene liked to go to South Beach for Memorial Day Urban Beach Week.

A Miami Herald video showed Eugene on the Miami end of the MacArthur Causeway shortly before 2 p.m. Saturday, naked and in an apparent drug-fueled rage. He straddled Poppo, punched him, tore off his clothes and gnawed at his face as at least four cyclists rode by and the newspaper’s surveillance camera rolled.

The carnage ended at 2:13 p.m., when Miami Police officer Jose Ramirez ordered Eugene to stop, and then shot him at least five times.

Eugene’s friends were stunned to learn of his involvement in the bizarre case. They described him as funny and friendly, with a particularly radiant smile. He was normal, and did not suffer from any mental illnesses, they said.

“He wasn’t homeless. He had a place to stay. He had a car, and he worked,” said Erica Smith, a close friend and former roommate of Eugene’s. “He had his ups and downs, but he was not an aggressive person. He was really sweet and giving.”

Smith said Eugene was down on his luck about five years ago with a string of arrests and a broken marriage, but recently was getting his life back together.

In 2004, North Miami Beach Police had to use a Taser to subdue him during a domestic dispute.

“He did smoke, I’m not going to lie about that,” Smith said. “Someone must have given him something really bad. A few days ago he told my brother that he was really depressed and didn’t want to live anymore. He was a guy who just wanted a family and someone to love him.”

Toxicology reports on Eugene’s body have not been completed. A Miami police union official speculated that he must have been high on LSD or some other drug that causes psychosis as the body overheats. As doctors and pundits hypothesized about what could have caused an ordinary man to do something so extreme, police said no tangible evidence to explain it had emerged.

Eugene graduated from North Miami Beach High in 2000. He lived off and on with his mother and friends and did an assortment of odd jobs, from selling CDs to working at McDonald’s and telemarketing. He last worked washing cars at an automobile dealership, Smith said.

Lately, he spoke of buying his own mobile car-wash business. His own late ’90s model Chevrolet Caprice was discovered Tuesday at an impound lot, after it was towed from South Beach.