There are many examples. And considering that other people are claiming that there are no modern examples, I'll provide some:
Cormac McCarthy, arguably the world's greatest living author. His real name is Charles.
Michael Crichton, Stephen King, Dean Koontz, Anne Rice, and J.K. Rowling have all used a pen name.
Louis-Ferdinand Céline, Lewis Carroll, Agatha Christie, George Orwell, Ayn Rand, Mark Twain and Dr. Seuss are all pen names.