Macduff, the Thane of Fife

In Shakspear's MacBeth, "Lay on MacDuff..." is a provocation to a fight. Is this popular phrase "Lead on McDuff" just a missquote and missuse of Shakespear, or was there really some popular "leader" named McDuff?

It has been quite a while since I read Macbeth, but wasn't MacDuff a powerful lord or thane, a feudal baron who performed militarily for the king?
Macbeth killed MacDuff's family and MacDuff cut off MacBeth's head and gave the head as a present to the lawful king, Malcolm.