Sexually molested his daughter, Billie
Attempted to kill John Black
Blackmailed Kate Roberts
Kidnapped Stefano DiMera
Drugged and attempted to rape his daughter, Billie
Curtis was the abusive husband of Kate Roberts, and father of her two children, Austin and Billie. When Curtis learned that his wife was sleeping with Bill Horton, he took their two children (then aged 4 and 2) and left her beaten and bloody on the side of a road, pregnant with another man's child. He told Kate that their children had died, and changed not only their names but his own (his real name is assumed to be Curtis Brown, but the real names of his children have never been revealed). Both Billie and Austin eventually broke away from Curtis, and ended up coming to Salem.
Their newfound happiness could have been destroyed when Curtis came to Salem to assassinate John Black on DiMera orders. Billie spotted her father and could have proven him as the shooter, but Billie lied to the police, terrified that Bo would find out that Curtis was her father, and that not only had he turned her into a drug addict, he had also sexually molested her as a little girl.
Once out, Curtis paid a visit to Kate Roberts, who had always believed that they had been divorced years ago. He taunted Kate with the deaths of their two children, never once telling her that they were already in Salem. Kate was shocked when Curtis told her that they had never actually divorced. Kate was desperate to hold on to Victor, so when Curtis blackmailed her with the knowledge of their marriage, she gladly paid up rather than risk losing her position in Salem society.
Curtis' last job in Salem was to bring Stefano DiMera to town so he could restart his reign of terror against the Bradys, but he decided to try to make a little money off of that as well, and kidnapped Stefano, holding him for ransom. He finally did return Stefano to his ward, Kristen, but by then, Curtis had already made an enemy for life.
When Curtis turned up murdered in an alley-way, all suspicion turned to Billie, whom he had drugged with the intent to rape that night. Kate soon became a suspect in Curtis' murder, and Lucas then claimed guilt to save his mother. At the same time, Kate discovered that Austin and Billie were the children Curtis had stolen from her so long ago. Eventually it was proved that none of the three had killed Curtis, and they went free. Stefano was ultimately responsible, but was never held accountable for Curtis' death.
Curtis returned twice as a ghost, once to take Marlena's soul to hell, and the second time to take Billie's soul to hell. He also appeared as a demon in the Garden of Eden storyline where Greta and Austin had to escape temptation to survive.