He set a ring record by making 14 successful title defenses. A record which stood for 27 years before Bernard Hopkins broke it. Monzon retired as undefeated champion in 1977. His record was 87-3-9 with 59 knockouts. He had won his last 80 straight fights.He won 31 times in a row. He had a lossless streak of 71, but had several draws in that time.
There is no evidence that he was paid to retire. He was in his mid thirties, which is a logical age to retire.
He was also an incredibly horrible human being and should be forgotten.
I watched the boxing news live at the time he retired, the WBC paid him 500k to retire, the WBA paid him an undisclosed amount. Yes, in his private life he was an a##hole, went to prison for killing his wife, died at 52.