3. Isaac Newton
I thought it'd be good for the Doctor to meet a famous scientist, but couldn't think of one off the top of my head. Luckily I was given a suggestion of Isaac Newton, and he's a great choice. He's done so many things in fields of maths and science, and that makes him an ideal match for the Doctor. But his most important discovery was of gravity, and this would probably be where the focus would be in an episode with him, seeing as that is what people know him for, especially children. Yes, he's a scientist, but so is the Doctor - imagine two scientific minds working together. Could it have been the Doctor that led Newton towards the name gravity? Maybe it wasn't an apple that fell from the tree but the Doctor accidentally landing the TARDIS in said tree and dropping his healthy snack - the banana! Yes these are far fetched, but it would be funny. Or maybe the apple was some sort of alien egg or bomb. The concepts are endless! Although as an afterthought, maybe he should meet a female scientist to encourage more girls to go into the scientific field.