10 Oldest Characters In The Doctor Who Universe
5. Mr. Sweet
Estimated Age: Over 65 million years.
Mr. Sweet - a surviving member of a species called the red leech - is a rather disgusting creature that debuted in Series 7's The Crimson Horror.
Attaching itself to the deranged Winifred Gillyflower, this particular leech's venom was used as part of a plan to poison the Earth, but with the Eleventh Doctor on hand, Gillyflower - along with Mr. Sweet - are both defeated.
But before he was smashed into a bloody pulp by Gillyflower's angry daughter, Mr. Sweet had lived an insanely long life. In the episode, Madame Vastra mentions that red leeches existed as far back as 65 million years ago, while the Doctor states that Mr. Sweet belongs in the Jurassic era, well over 100 million years ago.
Even on the conservative end of that spectrum, Mr. Sweet lived for at least 65 million years. Pretty good for something that looks so small and weak!