Clue: He generates huge interest seizing power — Richard III? (7)
Answer: USURPER
Explanation: Definition: Richard III?
An envelope ('seizing') pf P ('power') in USURER ('he generates huge interest'). The question mark definitely belongs to the "definition" part of the clue – firstly, as an indication by example, and secondly because historians differ as to whether Ricard was an usurper.