Abused Nicole Walker during the beginning of their marriage (not shown on screen)
Abused Max and his mother when Max was a young child (not shown on screen)
Pimped out his daughter Melanie to pay off a gambling debt (September 2008)
Blackmailed Nicole Walker into spying on Max (July 2008)
The early history of Trent Robbins was not shown on screen, but described later by the characters that encountered Trent years earlier. Trent was the biological father of Max Brady. According to Max, Trent, then referred to as "Trent Becker," was busy traveling with his job and did not have time for a family. Trent became abusive toward Max and his mother. His mother eventually died and Max escaped to Salem with Frankie. Trent did visit Salem once, but by then Max had been adopted by Shawn and Caroline Brady. Trent did not make any effort to get his son back.
When he was working on his PhD, Trent met a young college coed named Nicole Walker. Trent began courting Nicole and the two eventually married. Then, things turned ugly for the aspiring professor and his young bride. While never shown on screen, Nicole recollected that Trent was abusive during their relationship. He was so abusive that she eventually packed the only suitcase that she owned and fled. Nicole didn't look back, not even to file for divorce.
In the summer of 2008, Trent took a job as a professor of physics at Salem University. He began mentoring Nick Fallon and, through Nick, met a young bartender named Max Brady. Trent did not recognize his grown son and was quite disrespectful to Max because of Max's status as a "lowly barkeep." Max knew who Trent was and became increasingly angry around him. Desperate to discover anything from his biological past, Max broke into Trent's apartment and began searching for clues. Max found a picture of a young girl. Armed with his temper and the picture, Max confronted Trent. Trent begged Max not to tell anyone that he was Trent's son. Max agreed, but in return, demanded to know who the girl in the picture was. Trent refused. But, Max eventually found out that the girl in the picture was Trent's daughter, Max's half-sister. Max left for France to track down his half-sister, Melanie Layton.
Still determined to keep Max from meeting Melanie, Trent turned to Nicole Walker, his still legal wife, and blackmailed her into spying on Max. Nicole found out that Max was headed for France and informed Trent. Nicole agreed to do more favors for Trent in exchange for his silence about their marital status. If the news came out that Trent and Nicole were still legally married, Nicole would loose her huge divorce settlement from Victor.
Trent hired Steve Johnson to investigate the whereabouts of Nick Fallon (who had gone to France to help Max and Stephanie find Melanie). Steve saw right through Trent and asked Hope to run a background check on Trent. They discovered that Trent went by the alias Trent "Becker" for a while, and that he was married to Misty Circle (a.k.a. Nicole Walker). Meanwhile, Nick caught up with Melanie in France. Nick, Max, and Stephanie learned that Trent had been pimping out Melanie to pay for his gambling debts.
Trent made an ill-fated attempt to get a date with Marlena. Not only did she turn him down, but his advances angered John. John attacked Trent in the Brady Pub and told him to stay away from Marlena.
One by one, more people lined up against Trent. On September 26, 2008 Trent wandered up to a surprised Caroline Brady while she was visiting Shawn's grave at the cemetery. Trent had a knife sticking out of his back. He fell onto Caroline and died. The police found Caroline leaning over Trent's body and arrested her. The other initial suspects in his murder were: Max Brady, Nicole Walker, Melanie Layton, Nick Fallon, and Claude (the gambling shark he owed money to). Eventually, the Salem PD discovered that Nick Fallon was the one who stabbed and killed Trent. Nick had become addicted to pain pills and became obsessed with Trent's daughter, Melanie. Nick killed Trent because he knew that Trent was a threat to Melanie.