Q everyone knows Q, (John deLancie) He just turns up and harasses the USS Enterprise-D crew whenever it suits him. Q's one of several omnipotent beings who took it upon himself to test Federation lifeforms like captain Picard and remember poor Tasha yar? frozen solid like a snowcube.
Q states "what must I do to convince you people?"
Worf answer is priceless "Die"
Q "Very clever Worf, eat any good books lately?"
Live long and prosper.