Clue: Prime gatherer in extremis? (3,4,6)
Answer: THE GRIM REAPER
Explanation: Definition: Prime gatherer in extremis?
***(prime gatherer)** [anag:*in extremis*] and &lit. 
*I've never come across "in extremis" as an anagrind before, but as it can mean "in desperate circumstances", I think it's acceptable.