Bryan Steubing, 20, was shot shortly before 4 a.m. in the 3100 block of S. Main Street and transported to Orange County Global Medical Center, where he died.
Santa Ana police said a gunman walked up to the car and fired several times before taking off.
Steubing's grandfather described him as a caring person who was planning to celebrate his 21st birthday next month.
Police said they don't yet have a description of the suspect but believe the shooting is gang-related.
An investigation was ongoing.