The biker known as Wild Dogg was working on his motorcycle with a friend on Friday night in the California city when an SUV pulled up and a passenger opened fire, San Diego police Lt. Ernie Herbert said.
Fatal: Clyde Thompson Jr, of San Diego, the president of the local chapter of a national motorcycle club, was gunned down and killed on Friday
Loss: The local chapter of the Black Sabbath Motorcycle Club (pictured) that Mr Thompson led and rebuilt is mourning the death of their friend
He was apparently shot several times in front of the building of the group's 'mother chapter,' according to a post on the club's website.
Police haven't determined a motive for the killing.
Members of the group he led mourned and paid tribute to their friend, who was pronounced dead at hospital.
Black Sabbath Motorcycle Club mourned what it called 'Wild Dogg's martyrdom' in a post on the group's Facebook page.
'We continue to struggle to cope with the sobering reality that despite four decades of peaceful, non-violent existence,' the post said, 'we awake this Mother's Day Sunday having suffered the cowardly, brutal assassination of a Black Sabbath M.C. President, Wild Dogg.'
Mystery: Police haven't been able to figure out a motive or find a suspect in the murder of Mr Thompson, who was well-liked among his biker friends
'Reputation': Police are trying to find the person responsible as Mr Thompson's biker members say their club was known for staying out of trouble
It goes on to call Thompson a 'responsible brother with big shoulders. He was simply a very nice person who did not deserve to be shot down in the street like a rabid dog.'
Mr Thompson took charge of the local chapter in 2007, which was struggling, the club website said.
He retooled it and strengthened it with new staff, according to the website.
The club was founded in 1972 by seven black men who liked to ride on Sundays, the group's website said. The Mighty Black Sabbath M.C. Nation has since become a multicultural club headquartered in Atlanta with 17 chapters nationwide.
Late last year, Thompson took over what is known as the 'mother chapter' in San Diego.
Stunned: Mr Thompson's fellow club members are in shock as they mourn their president, who was shot in front of their chapter office
John, 'Black Dragon' Bunch, the group's national president who lives in Georgia, said members have historically been servicemen and tradesman - adopting nicknames to avoid misunderstandings with employers.
'We don't have a motorcycle club that has a reputation for trouble,' Bunch said to UT San Diego. 'So we can't imagine who would have the need or the desire to hurt one of our members.'
Bunch told the newspaper that Thompson, who led the club through a difficult period after taking over, 'was a problem-solver, he was not a troublemaker.'
Thompson was survived by a long-term girlfriend and two daughters, according to the club's website.