The man who put Charles Manson in prison is currently hospitalized in California, following complications from cancer surgery ... TMZ has learned.

Former prosecutor Vincent Bugliosi's wife tells TMZ, her husband underwent surgery back in April for stage 2 cancer.

According to his wife, the surgery appeared to be successful at first, but Vincent experienced complications shortly after, and was admitted to the ICU. Vincent's wife wouldn't specify the nature of the complications.

Vincent's wife adds, "He has been in very bad shape for some time. He regained consciousness this week, finally starting to be on the road to recovery. He's going to be in rehab for a long time."

Vincent left the ICU last week but is still hospitalized.

Thanks to Vincent's badassness back in the day -- Charles Manson was convicted of seven murders in 1971 and sentenced to death. Manson's death sentence was reduced to life in prison a year later when California abolished the death penalty.

77-year-old Manson's latest request for release was denied in April -- and since he's not up for parole again for another 15 years, chances are he'll die behind bars.