Penelope Wilton
Penelope Wilton built her career by starring in series. From the BBC sitcom Ever Decreasing Circles, she starred in from 1984 to 1989 to Downton Abbey, where she played the widowed Isobel Crawley from 2010 to 2015.
As far as series go, it doesn’t get bigger than Doctor Who in the United Kingdom, and Wilton even had a three-year stint as Harriet Jones in the series. She did appear in other films such as The Secret Rapture and also hit the stage for a play named Taken at Midnight, which won her the Olivier Award for Best Actress. She is currently filming the movie Downton Abbey 2.