The most shocking revelation details the Criminal Investigative Division's probe into allegations that Ali and Spinks fixed their two infamous 1978 fights.
Spinks stunned the boxing world by beating the champ during the first fight in February 1978 in Nevada, but then lost the heavyweight belt in a rematch the following September in New Orleans' Superdome.
"Top Rank Inc….planned to induce Muhammad Ali to throw the 2/15/78 fight with Spinks as well as a possibility of inducing Spinks to throw a subsequent rematch with Ali," the papers state.
The FBI files do not reveal the final outcome of the probe.
The documents also prove the FBI feared terrorists in Zaire would kidnap the fighters during the 1974 "Rumble in the Jungle" between Ali and George Foreman.
"There is a possibility of terroristic activity against the fighters in Zaire with even a ransom attempt as one plan of action," a September 24, 1974 memo reads.
For years, the FBI closely monitored Ali's every step, including a list of every one of his speeches as prominent member of the Nation of Islam.
However, ruthless FBI Director J. Edgar Hoover was terrified that his secret investigation targeting Muhammad Ali would embarrass him and the Bureau if the boxer found out.
The fear was spelled out in a May 13, 1966 memo to the heads of four field offices where he demanded to learn the identities of three Pakistani women seen with the champ at a Las Vegas hotel around the time he fought Floyd Patterson.
"It is not felt that we should conduct any investigation concerning his personal activities which could result in (Ali) Clay possibly charging the Bureau with harassment," the documents state. "If such investigations should come to Clay's attention, he might take action which could prove embarrassing to the Bureau."
