He is a Shakespearian actor who spent 16 years with the Royal Shakespeare Company , but is most famous for playing Jean-Luc Picard on Star Trek : The Next Generation . He also played Professor Xavier in the X-Men movies . He is most widely known for his television and film roles , such as Captain Jean-Luc Picard in Star Trek : The Next Generation , Professor Charles Xavier in the X-Men film series , and as the voice of Avery Bullock in American Dad !