In which TV series is Ari Gold a main character?

Who played Veronica Mars in 'Veronica Mars'? Who played Vincent Chase in 'Entourage'? In which TV series is Vincent Chase a main character? Who played Ari Gold in 'Entourage'? Who played Meredith Grey in 'Grey's Anatomy'? Who played Derek Shepherd in 'Grey's Anatomy'? Who played Cristina Yang in 'Grey's Anatomy'? In which TV series is Cristina Yang a main character?