Apparently has an unscrupulous past, details unknown
Borrowed money from a loan shark who worked for Joseph Sorel, in order to pay off his excessive gambling debts
When Mike first came to town, he was hired by Luke Spencer to work in Luke and Sonny Corinthos' blues club. Unknown to Luke he had just hired Sonny's father as his maître d'. Mike had left his wife and son when Sonny was still young, thinking that his son would be better off without him. Sonny's mother had re-married a cop, Deke, and Mike thought the Deke would be a better father to Sonny. What Mike didn't know was that Deke had beaten Sonny's mother and Sonny mercilessly. Mike tried to reach his estranged son, but Sonny ignored him. Sonny and Mike have had a turbulent relationship, as Mike tried to help Sonny through the tough times in his life, and Sonny has continually pushed Mike away. After much time, they managed to come to somewhat of an understanding. Mike opened the bar/restaurant, The Recovery Room, with former flame Mary Scanlon, a nurse at GH, and he now runs the restaurant where the interns at General Hospital often go to hang out.
When Caroline "Carly" Benson asked Jason Morgan to act as the father of her son, Michael, he had Michael christened and named him after Sonny, who was not living in Port Charles at the time. He also asked Mike to be Michael's godfather, which pleased Mike greatly.
Later on, when Ned Ashton, Alexis Davis, Chloe Morgan, and Jasper Jacks were trying to solve Chloe's problem with her uncle's will that said she had to be happily married or she would lose her company, they tried to get Mike to marry Chloe's evil Aunt Gertrude. Once Gertrude was married, she would no longer have claims to Chloe's company. Since Mike was conveniently single, they felt that he would be the perfect candidate. Mike agreed at first because of the large sum of money that Ned was going to pay him. But later, he learned just how unbearable Gertrude was and couldn't go through with marrying her. Also, he became interested in Tammy Hansen, an ex-prostitute who was now running Kelly's Diner.
Because of his compulsive gambling problem, Mike has run into financial trouble in the past and has gone to Sonny or Jason for help. One time in particular though, Mike didn't want to upset Sonny, so he went to a loan shark instead. What he didn't know, was that the loan shark was employed by Sonny's archenemy, Joseph Sorel and because he couldn't pay back the loan quickly, Sonny was in grave danger. When Carly tried to fix the situation, she ended up only getting Sonny in more trouble, and the two were forced to get married in order to prevent her from testifying against him. After this, Mike disappeared. Carly could tell that it was hurting Sonny and also Tammy, so she made it her mission to find Mike, and she did, on Cortlandt Street. She gave him money and got him to come back home where he is continuing to build his relationship with Tammy.
Mike and Tammy eventually broke up and Tammy left Port Charles. Mike again is single. Sonny and Carly have divorced and Mike has become a close ally with Carly. Carly tries to take care of Mike because she knows he's a good person who makes bad choices like herself. She also knows that Sonny loves his father deep down and wants them to be closer. Mike has been helping Carly keep AJ away from little Michael. Mike made another mistake and it come to light recently. A woman named Janine Matthews came to town to blackmail Edward Quartermaine for money and ran into Mike. Evidently they knew each other but no one knew how until Janine's daughter Courtney came to town looking for her mother. Sonny had Janine put up in a nice hotel to try to get her to do what he wanted for Edward so when Zander found Courtney who said she was looking for Janine he took her to Sonny. While there Mike and Janine both arrived and Courtney recognized Mike as her father and Sonny was shocked. Evidently, Mike and Janine had a fling in Vegas and Courtney was the result. Mike walked out on them just as he did Sonny was he was young but Janine told Courtney that Mike had died. Courtney was shocked to see him and Sonny was angry that Mike could do that again to another child. Mike again gave the excuse that he felt they were better off without him so he left.