8. Rowan Atkinson - Blackadder
The brilliant central conceit of legendary Brit comedy series Blackadder is that Rowan Atkinson portrays a different member of the Blackadder dynasty in each series, no matter that the characters generally share a number of character traits both detestable and hilarious.
In the show's first series, he plays the dim-witted yet highly ranked Prince Edmund at the end of the British Middle Ages, while in Blackadder II he takes the role of Edmund's considerably smarter great-grandson Lord Blackadder during the reign of Queen Elizabeth I.
For Blackadder the Third, set during the Georgian Era, Atkinson portrays Mr. E. Blackadder, Esquire, a butler to the Prince Regent and by far the most cunning of all the Blackadder iterations - enough that he actually survives the events of the series and is implied to become King George IV.
For the fourth and final series, Blackadder Goes Forth, Atkinson then played the cynical, caustic British Army Captain Blackadder during World War I.
His tenure didn't quite end there, though: in 1988's Christmas special episode, Blackadder's Christmas Carol, he assumed the guise of Mr. Ebenezer Blackadder, the apparently nicest man in Victorian England, and in 1999's short film Blackadder: Back & Forth, he played a modern day Lord Blackadder who attempts to change history in his favour.
This is without even counting minor members of the Blackadder family who've been briefly featured, ensuring that Atkinson has played a bevy of separate-but-similar characters throughout the show's run.