悲观主义者 in English:

The optimist looks into a mirror and becomes more optimistic, the pessimist more pessimistic.

There is no sadder sight than a young pessimist, except an old optimist.

But consider what will happen if the pessimists are wrong.

Dr House, from the hit TV series House M.D., is famous for being a pessimist.

There’s no need to be a pessimist! Things will get better soon!

I am by turns an optimist and a pessimist.

Always borrow money from a pessimist; he doesn't expect to be paid back.