Steven Halperin, 64, apparently waited for traffic to clear before making a sharp turn and speeding into Lake Michigan at approximately 10:30 pm Thursday night.
Witnesses on Lake Shore Drive say the car went across a bike path, down steps and then went directly into Lake Michigan.
Divers had to break the car window because the door was locked. They pulled Halperin out of the water and performed CPR, but he was later pronounced dead at Northwestern Memorial Hospital, according to the fire department.
''As the car passed, he continued to go. He came across the curb, and I saw it as the car went down the stairs,'' said Kimberly Brown, a witness.
Halperin was a resident of the South Loop. He loved the water and spent summers on his family boat. His wife, Mary, says it was ironic that Lake Michigan took his life.
''He was always looking for a good time, just walking down the lake doing whatever, he loved the city,'' said Mary Halperin.
She wants her husband to be remembered for his volunteer work, teaching disabled students how to sail.
Halperin was a retired salesman and an overnight doorman at a high-rise building in Uptown.
At the time of the accident he was on his way to his doorman job in the Uptown neighborhood.
''He was always a nice guy, he used to greet me every time I came in, and used to hold the door for me,'' said Harshad Gado, a resident of the Uptown building. ''We used to chat sometimes,'' he said.
Halperin's wife says her husband had epilepsy and may have suffered a seizure while driving.
''I believe it was health issue, he was not depressed, he was not unhappy, he wasn't sad, I'm convinced it was a health issue," she said.
Police are calling this a death investigation. Halpern's wife says the autopsy is scheduled for Friday afternoon.