Marilyn Monroe and Frank Sinatra
Sinatra and Monroe had turned to each other for comfort many times during her career especially in the latter years of her life with the pair being on-again, off-again lovers for nearly a decade. Sinatra was always giving Monroe gifts. He gave her a pair of diamond studded earrings valued at $35,000 and moved her into an apartment building managed by Frank Sinatra's accountant, Harry Ziegler. Sinatra, on another occasion, gave Monroe a poodle instead of a diamond engagement ring, which is what she thought Frank was giving her in the early days. Marilyn always hoped that a friendship with Frank would lead to marriage, but it was never to be. Dolly [Natalie] Sinatra, Frank’s mother, liked Marilyn because she had a good appetite and wanted Frank to marry her because she was a bigger star than Mia Farrow. However, fastidious Frank was put off by Marilyn’s disgusting personal habits which left stains on his furniture. Frank liked Marilyn as a person and a friend, but could also be very cruel to her, as he was to most women at one time or another. Frank insisted she keep out of sight when she was staying at his place and one evening, drunk on champagne and tired of waiting for him, she wandered nude into the room where Sinatra and his friends had a poker game going. Furious, he hissed: "Get your fat ass upstairs!"

Frank had a strained friendship (that ended upon Marilyn's death as he held Frank partly to blame) with Marilyn’s 2nd husband, Joe DiMaggio but despite this helped him stage a raid on a stranger's apartment as Joe believed that Marilyn was in the apartment with her lover. This "Wrong Door Raid" led to a successful law suit against DiMaggio and Sinatra. The friendship between the two ended when Sinatra had an affair with Marilyn.

The two weren't having sex when they first moved in together, however that changed when Sinatra came downstairs one night and saw Marilyn naked in the kitchen. Sinatra never considered popping the question although it is rumoured that a few weeks before Monroe's death, Sinatra considered popping the question in an attempt for Marilyn to get her life back on track as "No one [would] mess with her if she is Mrs. Frank Sinatra." The weekend before her death, Sinatra reportedly tried to convince Monroe to start her life over. "Why bother?" she responded. "I'm not going to be here too much longer." Sinatra felt that if she were his wife, everyone else would back off, give her some space and allow her to get herself together. However, Marilyn was planning on marrying Joe DiMaggio for the second time, so Sinatra’s proposal was too little too late.

Frank was one of the people who coaxed Marilyn to the Cal-Neva Lodge the weekend before her death. Frank helped the Kennedys take photos of Marilyn being molested by prostitutes in an attempt to blackmail her if she went public with her affairs with the Kennedy brothers. Frank did care about Marilyn, as he tried to get her to forget about the Kennedys and forget about planning her revenge by destroying their image, but when she wouldn’t listen Frank lured her to Cal–Neva in an attempt to almost make her see sense, get over the Kennedys and move on – providing her with the “you’ve got to be cruel to be kind” method of support. Marilyn was deeply hurt that someone she considered a friend was working against her, and changed her opinion of Sinatra after that. One week later she was dead.