Who played Negan in 'The Walking Dead'?

Who played Rick Grimes in 'The Walking Dead'? In which TV series is Rick Grimes a main character? Who played Daryl Dixon in 'The Walking Dead'? In which TV series is Daryl Dixon a main character? In which TV series is Negan a main character? Who played Nucky Thompson in 'Boardwalk Empire'? In which TV series is Nucky Thompson a main character? Who played Violet Crawley in 'Downton Abbey'?