He was in a school band with his friend Mike Ruby and then Marshall Bruce Mathers (Eminem) thought it was a good idea to call the rap duo M&M (no pun on the company , though may be.Its Eminem we are talking about… ). read more
Its just a wordplay of his original name “Marshall Mather “ , its initials spell like MnM which sounds like Eminem . hence the name “ Eminem “ Some fans theories even suggest reading Eminem backwards means “ Men In Me “ not exactly but kind of read more