Mark Evans is a minor fictional character in J.K. Rowling's Harry Potter series of novels. He is mentioned only briefly in one novel, Order of the Phoenix. On page 13 (American) the book says:

"So who've you been beating up tonight?" Harry asked, his grin fading. "Another ten-year old? I know you did Mark Evans two nights ago."

The general speculation among Harry Potter fans is that Mark is a relative of Lily Evans Potter in some way, and, as he is ten, he will be entering Hogwarts next year. If this turns out to be the case, it illustrates the manner with which Rowlings uses plot devices and foreshadowing to add credibility to new characters.

Another very similar example is in book four when Harry and the Weasleys are on their way to the World Cup, Amos Diggory mentions a family that lives nearby called the Lovegoods. Luna Lovegood isn't formally introduced until the next book.