joker
noun /ˈdʒəʊkə(r)/
  /ˈdʒəʊkər/
Idioms - a person who likes making jokes or doing silly things to make people laugh- He’s always been a bit of a joker.
 
- (informal) a person that you think is stupid because they annoy you                                     
- an extra playing card that is used in some card games, usually as a wild cardTopics Games and toysc2 enlarge image enlarge image
Word Originearly 18th cent.: from the verb joke + -er.
Idioms 
the joker in the pack 
- a person or thing that could change the way that things will happen in a way that cannot be predicted
