You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: HISTORIC ROYALTY 
Clue: These two men seen here, allies during World War I, were sometimes mistaken for each other
czar nicholas ii & king george v

Category: MUSIC LEGENDS 
Clue: His 2003 People magazine obituary was headlined "Fade to Black"
johnny cash

Category: NOTABLE NAMES 
Clue: He declined the offer to lead a country & once said, "Politics is for the present... an equation is... for eternity"

albert einstein