1. Elisabeth Sladen as Sarah Jane Smith
The longest serving companion on the original classic series. The first companion from the old series to re-appear in the new Doctor Who. Elisabeth Sladen is pretty much unanimously considered the most beloved of all actresses to play the Doctor's companion, and this turned into her having her own series following her re-appearance. Sadly, Ms. Sladen passed away from cancer in 2011, but her role on Doctor Who as Sarah Jane Smith will outlast all of us.