Mardin is a student of Wellston Private High School and attends the same Trigonometry class as John and Remi. His first appearance is in Chapter 1where he heckles John before the trigonometry teacher threw a piece a chalk at him, causing his nose to bleed. In Chapter 36, it is revealed that he and Hower were partners in a literary analysis project. Chapters 82 and 83 reveal that Mardin is a resident of Wellston's boys' dorms and acknowledges Zeke as the dorm's "ruler." He and Zeke "welcomed" John to the dorms.[2][3]

Don't have any specific voice for him, just try to make him sound like a stereotypical bully.