It's impossible not to love a robot dog that practically screams "I'm from the seventies". He's sassy, too. A robot dog with sass? Best. Idea. Ever. K-9 was so popular that he eventually ended up being part of David Tennant's run. Along with the scarf, it's possible to get merchandise featuring K-9. Usually it's in action figure form, but it still counts. It would've been unforgivable not to include K-9 on this list because he was such a huge part of the Fourth Doctor's era. He was part of what made the Fourth Doctor who he was and he is an emission of the years of Tom Baker. What's more, who wouldn't want a talking robot dog as their faithful companion? Affirmative!