Jack Finnegan (father)
Li Finnegan (adoptive mother)
Sheila Carter (presumed biological mother)
Hayes Forrester Finnegan (son; with Steffy; 2021)
Punched Vinny Walker 
John "Finn" Finnegan is a doctor who treated Steffy Forrester, the CEO of fashion house Forrester Creations, after she sustained injuries in a motorcycle accident. Finn found himself visiting Steffy after she was released from the hospital and noticed she was having a difficult time caring for herself and her young daughter, Kelly. Finn agreed to prescribe Steffy one more bottle of pain pills but refused more. Finn acknowledged his attraction to Steffy and offered to stop treating her for ethical reasons, but Steffy wouldn't hear of it.
Finn was surprised when Steffy's protective ex, Liam Spencer, began questioning Finn's motives. But Finn was even more surprised when Liam recruited him and Steffy's father, Ridge Forrester, for an intervention because Steffy had become addicted to painkillers she had gotten outside of Finn's care. With Finn's help, Steffy agreed to go through rehab and took the treatment quite well.
When Steffy came home, Finn arranged for Kelly to be there, which earned Liam's ire. Finn reciprocated when Steffy professed her love for him and was satisfied when Liam returned acknowledging his jealousy and promising to stay out of Steffy's personal life. Later, Finn found it odd when Steffy's brother, Thomas Forrester, who had a history of mental imbalance and obsession with Liam's current wife, Hope Logan, went on a tirade warning Finn that waffling Liam always cycled back around to Steffy eventually; seeing Liam's adversarial attitude about Thomas, Finn began to wonder if Thomas was right, even blowing off the news that Thomas was keeping a mannequin made to look like Hope in his apartment. However, Finn visited Thomas and saw that he was most definitely unwell, later learning that Thomas had kissed the mannequin and collapsed due to bleeding in his brain.
Finn was rocked when he learned that Steffy had slept with Liam, who had thought Thomas had kissed Hope. Discovering Steffy was pregnant and not sure if Finn or Liam was the father, Finn stood by Steffy and hoped her paternity test would prove him the parent. When the test confirmed Liam instead, Finn remained at Steffy's side but became less certain of how he now fit into Steffy's life.
Finn walked into the hospital lab one day and came across Thomas with his best friend Vinny Walker, who had just confessed to tampering with Steffy's test. Finn punched Vinny to keep him from escaping, then learned Steffy wanted to leave town so Finn wouldn't have to endure Steffy carrying Liam's baby. Finn stopped Steffy and happily informed her that he was the baby's father instead, proposing marriage to her on the spot. Finn received a shock when he came upon Vinny lying on a slab in the hospital morgue; someone had run Vinny over with a car and left him for dead. Finn called Thomas to confirm Vinny's identity. Finn later learned that Vinny had thrown himself in front of Liam's car to frame Liam and clear the way for Thomas to have Hope.
Finn and Steffy learned they were having a boy, whom Steffy gave birth to via a water delivery. Finn asked Steffy for an impromptu wedding, but hedged when Steffy said she wanted to meet Finn's parents first. Finn's father, Jack Finnegan, arrived unannounced, and Finn admitted to Steffy he had been adopted. With his adoptive mother, Li Finnegan, also at his side, Finn exchanged vows with Steffy. But when Finn excused himself to the Forrester guest house to call in about a patient, he was approached by a woman claiming to be his biological mother. Excited to finally know his real mom, Finn introduced the woman to the Forresters, only to learn she was Sheila Carter, who had committed numerous crimes against that family, including causing Steffy's mother, Taylor Hayes, to be presumed dead for years after Taylor and Sheila struggled over a gun.
Finn agreed with Steffy's pleas to distance himself from Sheila; when Finn received a text from Sheila, Finn replied with a heart emoji, figuring the lack of further response would discourage her. Finn confided in new roommate Paris Buckingham about his contact with Sheila and was appalled when Jack demanded that Finn let Sheila hold Hayes while Steffy was out of town. Finn gave in, but when Steffy came home unexpectedly and caught Sheila with Hayes, Finn found himself ordered out of the house by Steffy, who declined to file their marriage certificate. When Finn told Sheila to stay away, Sheila fainted, but Finn didn't believe Steffy's contention that Sheila was faking an ailment. After his fellow doctors couldn't find anything wrong with Sheila, Finn again rejected his birth mother, who sent him another text; Finn admitted to Hope that he still wanted to get to know Sheila.