As Odion's Mystical Beast of Serket destroys Joey's monsters one by one, he is impressed by the friendship Joey shares with the others, and recounts his and Marik's own dark history; revealing himself to be Marik's older, adoptive brother who was mistreated by their father for not being a true member of the tomb keepers, and that he dedicated his life to protecting his brother from his inner evil.
Yu-Gi-Oh! Greek Forum