In a civil suit, the person who files suit and the person against whom the suit is filed are called

The correct choice is: “plaintiff, defendant”

In a civil suit the person who institutes the suit (by filing a plaint) is the plaintiff, and the person against whom relief is sought is the defendant. “appellant, respondent” are the parties in an appeal; accused and prosecutor are terms of a criminal case (and in the reverse order); “accuser” is not the term used in a civil suit.