Leo Stark (Greg Rikaart) was introduced to "Days of Our Lives" viewers in March 2018. The character came to town on a mission from Vivian Alamain (Louise Sorel) to seduce Sonny Kiriakis (then Freddie Smith) and ruin his career as CEO of Titan Industries (via Soaps in Depth). The two began dating, and Leo even wormed his way into a job at Titan. Once the couple became intimate, though, Leo hit Sonny with a sexual harassment lawsuit and started attacking other areas of his life as well. Leo then tried to blackmail Sonny into marriage in exchange for staying quiet and saving his company.

Meanwhile, Sonny's longtime love, Will Horton (Chandler Massey), foiled the plan and got into a heated physical altercation with Leo. The fight ended with Leo falling into a fireplace and hitting his head. Sonny and Will believed Leo was dead and tried to cover up their crime by hiding his body.

However, Leo eventually showed up alive, shocking the couple, and threatened to tell all of Salem what they'd done to him. Although Leo was a thorn in Will and Sonny's side, everything eventually sorted itself out between the trio. However, it became clear that Leo's quest to take Sonny down wasn't the only thing he was hiding when Will tracked down his mother.