Massimo Marone got his education at Northwestern University in Evanston, Illinois, where he met Stephanie Douglas. Massimo fell for Stephanie, who was involved with Eric Forrester; however, Eric was interested in Beth Logan. Massimo and Stephanie went their separate ways when Stephanie got pregnant and married Eric; Massimo eventually came to run shipping conglomerate Marone Industries.

Massimo arrived in Los Angeles to expand his business and reconnect with Stephanie, who had stayed in touch with Massimo without Eric's knowledge. Massimo ran afoul of Eric, co-founder of design house Forrester Creations, and denied Eric's contention that Marone Industries was linked to the mob. Massimo knew Stephanie wanted to be rid of Eric's ex-wife, Brooke Logan, who was now pursuing Stephanie's married son, Ridge Forrester; when Massimo blamed Eric for Stephanie's problems with Brooke, Massimo found Eric's fist in his face. Still enamored of Stephanie, Massimo offered to get Brooke out of the way; Massimo located Brooke's father, Stephen Logan, in Paris and paid Stephen $5 million to feign health problems in order to convince Brooke to join him overseas. Massimo gained an enemy in Ridge when his machinations were discovered.

Massimo and Stephanie reminisced about a final evening they'd shared before Stephanie married Eric. Massimo called 9-1-1 when Ridge confronted Massimo in his office and hurt himself badly, after which Stephanie began acting strangely. Massimo was stunned when Stephanie confessed that blood work revealed Massimo was Ridge's father, not Eric! Massimo was thrilled until Stephanie swore him to secrecy; instead, Massimo decided to groom Ridge, who was having problems at Forrester, to take over Marone Industries. To force Ridge into coming over to him, Massimo trained Ridge's half-brother, Rick Forrester, to compete against Ridge in the boardroom.

Massimo romanced longtime friend Sally Spectra to keep her from discovering Ridge's paternity, then told Stephanie if he couldn't have her, he would have Ridge. Massimo hired Ridge at Marone and made him his sole heir. Getting nowhere with Stephanie, Massimo met a mysterious woman in a bar and had a tryst with her, granting her request to take her out of the country. But Massimo got the shock of his life when Stephanie heard the woman's voice on Massimo's answering machine and realized he had been seeing Sheila Carter, whose extensive criminal history included trying to kill Stephanie. Massimo and Stephanie rescued Rick's wife, Amber Moore, who had been framed and kidnapped by Sheila to clear the way for Sheila's daughter, Erica Lovejoy, with Rick.

In Portofino, Italy, Massimo fumed over the growing closeness between Brooke and Ridge, whose wife, Taylor Hayes, had just died from a gunshot wound sustained by Sheila. Complaining to Brooke's daughter, Bridget Forrester, Massimo let it slip that Ridge was his son. When Bridget realized that she and Ridge weren't related after all, Massimo encouraged Bridget to pursue Ridge to get him away from Brooke; as extra insurance, Massimo tasked Brooke's ex-lover, Deacon Sharpe, with seducing Brooke away from Ridge. But after Stephanie tried to discourage Ridge and Bridget's burgeoning feelings by sending medical student Bridget away for education in Copenhagen, Massimo told an incredulous Ridge that Eric wasn't his father.

One of Massimo's tankers went aground, so Massimo went to Mexico to confront its captain, Nick Payne. Massimo met Nick's mother, Jackie Payne, and didn't immediately recognize her, but when Massimo saw that he and Nick wore the same signet ring, Massimo remembered having a fling with Jackie and found out Nick was his son only after Jackie admitted it during a plane crash. Massimo hired Nick at Marone and tried to get him interested in Brooke, who was reuniting with Ridge. Massimo had Eric removed by security guards after the furious Eric learned the truth about Ridge's paternity.

Bonding over Nick, Massimo and Jackie renewed their romance and got married. Soon after, Ridge was kidnapped; Massimo tracked him to South America and was shocked to find Ridge being held captive by Sheila. Before a mêlée ensued in which Ridge was presumed dead, Massimo was introduced to his apparent daughter with Sheila, Diana Carter. Massimo celebrated when Ridge turned up alive, but worried his family would be torn apart after Nick and Brooke's "grief sex" left her pregnant. Elsewhere, Massimo had his hands full with his rebellious nephew, club owner Oscar Marone, whose illegal business practices were responsible for the death of singer Macy Alexander.

As Massimo refereed his sons fighting over Brooke, Massimo became jealous of Jackie's friendship with Eric and hired Deacon to dig up dirt on him. Massimo then brought to town James Warwick, a psychiatrist friend of the Forresters, to advise Brooke in her choice between Nick and Ridge. Massimo began to suspect Jackie of having an affair and caught her on the phone with Deacon, so Massimo held a gun to Deacon's head, then hired him to find out who Jackie's lover was. On the day of Nick's wedding to Brooke, Massimo and Nick were arrested for bribing foreign agents based on information Ridge found on Nick's computer, but they were ultimately released for lack of proof.

When it came out that Ridge was the father of Brooke's baby after all -- and that Jackie knew about it -- Massimo served Jackie with divorce papers, but soon forgave her and bought her a chain of department stores, which he rebranded Jackie M. Massimo was about to make Deacon president of Jackie M when he learned of Deacon's affair with Jackie and suffered a stroke, rendering him unable to speak. Massimo plotted his revenge as Deacon, who believed Massimo was unaware of his surroundings, flaunted his affair with Jackie in front of Massimo and drugged Jackie to taunt him. After Nick arranged for Massimo to undergo experimental treatments utilizing electrical impulses, Massimo recovered and tormented Deacon with a gun, then laughed as he revealed it was loaded with blanks.

Massimo divorced Jackie, then spiked recovering alcoholic Deacon's drink as revenge, causing Deacon to fall off the wagon. Massimo supported Nick when he decided to move on with Bridget, then flew off to Italy to rescue Ridge, who had been kidnapped by obsessive ex-girlfriend Morgan DeWitt. Massimo reestablished a friendship with Jackie, but ultimately decided not to reunite with her. While standing in as a witness for Stephanie while she removed stocks from her safe, Massimo discovered paperwork that named Stephanie as the sole owner of Forrester Creations; Massimo contacted Genoa City billionaire Katherine Chancellor, who confirmed a trust established by Stephanie's father, John Douglas. Massimo was on hand as Stephanie kneed Eric in the groin for his deception.

Massimo thought he finally had a chance with Stephanie until she went back to Eric. After Ridge had a heart attack, Massimo changed his tune and threatened Brooke, warning her to steer clear of Nick, who wanted Brooke back. Massimo bribed Forrester secretary Megan Conley into helping him frame Jackie for tax fraud, tax evasion, and money laundering, then promised Jackie he'd clear her if she helped keep Brooke and Nick apart for Ridge. Massimo faced Nick's wrath after he caught Massimo and Megan conspiring together, and Massimo was removed as CEO of Marone Industries.

Massimo disappeared from the canvas after he and Stephanie tried and failed to stop Nick's wedding to Brooke by publicizing nude outtake photos from her Brooke's Bedroom lingerie line. Though Massimo hasn't been seen since 2006, he is often referred to, usually by characters who remind Ridge he is not really a Forrester.