Doctor Who: Every Post-Regeneration Episode Ranked Worst To Best

Karate chopping a brick in half, a burst of running on the spot, and a bout of skipping is all the Fourth Doctor needs to get going and straight into the action. A recovery sleep and deep introspection is not for him; just a fedora over the face, power naps and Jelly Babies. In fact, the Doctor does tell the Brigadier that he "must cultivate a sense of urgency".

Although Robot is far from perfect - K1's enlargement from Iron Man Mark I to Rita Repulsa 'make my monster grow' is rather slapdash - but it's a ridiculously fun episode to introduce Tom Baker's bonkers bohemian incarnation.

The season 12 opener has a childlike action-packed energy about it; you could imagine playing with your UNIT toy soldiers trying to stop a giant homemade rampaging robot made out of your mum's tin foil. Don't forget to add some remarkable stealth-like qualities to the clunking feet that be-lie its wildly gesticulating motions. Then throw in a stereotypical madcap professor and a classic countdown clock to nuclear oblivion to which the Doctor averts by two seconds for good measure.

You can see that childlike imagination in the Doctor's widest-eyed enthusiasm. Baker is wonderfully wacky and fizzes with an alien elan, which is funnily encapsulated during his impressively speedy outfit changes from Viking warrior, the King of Hearts, a pierrot clown, to... bravo Brigadier for saying "much better" at the fourth look. That carefree joie de vivre is perfectly summed up as the Doctor embarks on new adventures with our best-loved companion:

SARAH: Doctor, you're being childish.

THE DOCTOR: Well of course I am. There's no point in being grown up if you can't be childish sometimes. Are you coming?