While going to the funeral for Rebekah's lover, Emil. Klaus, Elijah, and Rebekah witnessed a man whipping a young boy, and the boy turned around and thrown an apple at him, clearly angered at his treatment. The Man turned to continue whipping, but Klaus stepped in and made the man stop beating the boy by killing him on sight. Klaus approaches the boy and tells him that he is a survivor, before asking for his name. The boy says he hasn't been named as his mother didn't want to name him until he was 10 years old in fear of him dying of fever, although she died before he could be named. Klaus listened to his story and named him Marcellus, the name meaning "Little Warrior".
Klaus decides to take the boy under his wing, 'adopting' him. When growing up, Marcel takes a liking to Rebekah. Marcel is telling Klaus that nothing is going on with him and his sister. He however afterwards did admit that he likes Rebekah but says that he’s never acted on it. On the other hand, Klaus' bond with Marcel kept him from killing him, despite having warned him to stay clear of Rebekah. Marcel wants to be part of the family as a vampire, with the intent of having Klaus himself do the honor by becoming his Sire. After discovering Marcel's and Rebekah's hidden relationship, Klaus makes Marcel choose: To live a happy life with Rebekah as a human or to become a vampire. Marcel chose Rebekah, and Klaus left Rebekah neutralized for fifty two years.
- Marcel met Klaus when he was 10 years old.
- Klaus freed Marcel from slavery.
- Klaus didn't know Marcel was alive until he came back to New Orleans looking for the witches conspiring against him.
- Marcel chose Klaus over Rebekah.
- Aside from Stefan Salvatore, Marcel appears to be the only lover of Rebekah's that Klaus hasn't killed. He did, however, dagger Rebekah over their affair, saying that she "needs a lesson on what she can and cannot take from him", implying that he doesn't want to share his "son" with his sister.
- Klaus reveals after he assumed Marcel had died in the fire at the Opera House in 1919, it was years until he could speak his name.