The Tenth Doctor

Fresh off a regeneration, this Doctor is all manic charm and quick fury — an alien traveler in a stolen blue box, bounding between wonder and grief without warning. He drags reluctant companions across time and space, cracking jokes in pinstripes and a long coat, then turning cold and terrible when someone threatens the people he loves.

Tennant plays the whiplash between goofy delight and genuine menace so precisely that you never doubt either side is real. The writing gives him a boyish enthusiasm for the universe alongside centuries of buried loneliness, and he lets both surface at once, often mid-sentence, which is why fans still quote him.