ringleader - Someone who is the main influence or motivator behind a particular action or event, especially a disruptive or controversial one.
The police managed to arrest the ringleader of the gang, who had coordinated the series of robberies across the city.
unforgiving - Not making an allowance for error or weakness in others; not willing to forgive others for things they might have done wrong.
Because they knew that Alaska in the winter is an unforgiving environment, they had to plan their expedition very carefully.
