Whenever you are watching or re-watching a Doctor Who episode or one of the Harry Potter films, you are most likely to come across some familiar faces. Just like the BBC loves to re-use prop sets, demand and supply of British actors seems to run short sometimes as well. That moment where you are pointing at your screen and nudging your friend shouting "That's Dumbledore from Harry Potter! What's he doing here! Why is he being so mean!?" It happens to the best of us. Not to mention the potentially excellent material this can provide for the crossover theorists among us. Maybe there was just a very disappointed 11 year old Time Lord on Gallifrey who never received his Hogwarts letter so decided to steal a TARDIS and explore the universe. After all, who needs magic when you have a blue box that's bigger on the inside and can take you anywhere in time and space, right? Whether they portray the bravest of heroes or the brilliant villains fans love to hate, every single one of these actors have left their ever remaining mark on two of the biggest and most adored fandoms the world has ever known. Because of that, they have earned our love and loyalty... always.