Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

Who has written a series of novels, entitled The Dark Tower, of which the first, in 1982, was entitled, The Gunslinger?
the dark tower

Which Union leader of the American Civil War gave his name to a tree in California's 'Sequoia National Park'?
american civil war

Appointed in April 2012, what is the name of the current manager of Barcelona Football Club ?

barcelona