8:54 AM PT -- Robert De Niro just issued a statement on LaMotta's passing, "Rest in Peace, Champ."
Jake's wife tells TMZ, Jake died in a nursing home due to complications from pneumonia.
Another family member tells TMZ, Jake's condition deteriorated in the last few weeks. He was put on a feeding tube, which he kept pulling out. His condition worsened considerably in the last few days and a decision was made to withdraw the tube.
Jake's wife tells TMZ, "I just want people to know, he was a great, sweet, sensitive, strong, compelling man with a great sense of humor, with eyes that danced."
LaMotta was 83-19 in 106 pro fights -- a career that began in 1941, after he was rejected from serving in the military due to a medical issue.
He went on to win the world middleweight championship -- but he's most well known for his 6-fight rivalry with Sugar Ray Robinson ... though he only won 1 of the 6 fights.
LaMotta was famously portrayed by De Niro in the 1980 movie "Raging Bull," based on Jake's autobiography. De Niro won the Academy Award for Best Actor that year.