Mr. Seyton

Mr Seyton is the true main antagonist of the Doctor Who Big Finish audio drama The Kingmaker. A time-travelling "soothsayer" in the service of Duke Richard of Gloucester, Seyton has pledged his allegiance to the ambition monarch and provided him with knowledge of future events - claiming that without his advice, England will be brought down from within by the scheming Woodvilles and eventually conquered by the French. However, Seyton is quite clearly using Richard for his own ends, and will not stop until he is certain that the Princes in the Tower have been killed.

He was voiced by Michael Fenton Stevenson

In Defence Of Elizabeth
Unknown to all but a few, Mr Seyton is none other than William Shakespeare