Valentin was thought to be the disowned son of Mikkos Cassadine when he first came to Port Charles, and he was a villain. He took Sam, Jason, Ava, Laura, Kevin and Nikolas hostage at Wyndemere and shot Nikolas, who fell out of a window. He was presumed dead for years. He also shot Kevin and left them all there. Then he met Nina. Enchanted, he had a one-night stand with her and later returned to woo her. He tried to kidnap Spencer but was caught and arrested. He returned and claimed the Cassadine inheritance, including Wyndemere, as his own. He also claimed his daughter, Charlotte, whom Griffin thought was his. He and Nina were together for a while. Nina and Charlotte loved each other as well.
Nikolas returned in 2020, and he reclaimed Wyndemere. Eventually it was revealed that Victor and Helena were actually Valentin’s parents. Also, Lulu Spencer was revealed to be Charlotte’s biological mother. There was a lot of conflict between Nina, Valentin and Lulu, and between Valentine with Laura, Spencer and Nikolas. Also, Valentin played a cat-and-mouse game with Anna, leaving clues about their past. It turned out that he had some major deformities as a child, but he went to work for the DVX. He blamed Anna for rejecting him when he tried to kiss her. Later, they determined that it was her twin sister, Alex, not Anna, that had rejected him.
Meanwhile, Nina divorced Valentin because she blamed him for her brother’s death. He tried to win her back with lies, so she rejected him. He wormed his way into ELQ, with the help of lawyer Martin. Later, his father Victor threatened Charlotte if Victor didn’t do his bidding, including poisoning Laura. Valentin couldn’t go through with it. His years spent in Port Charles, along with his love for Charlotte and Nina, have made him a better person. Valentin worked with Anna to protect Charlotte and get rid of Victor. Along the way, they fell in love. Valentin went from villain to hero.