8) Martha Jones
Whoever followed up Billie Piper’s Rose Tyler after she left at the end of season 2 was always going to have a tough job. As such, Freema Agyeman’s Martha Jones is often overlooked by fans, as she only lasted a single season as a full time companion. This is a great shame, as Martha is actually a terrific character.
A trainee doctor herself, Martha’s story arc revolved around her unrequited crush on the Doctor. While he was still pining after Rose, he was unaware that his new best friend had developed feelings for him. Though this romantic angle put off some viewers, it made Martha a very sympathetic character.
Let’s not forget, though, that Ms. Jones is also incredibly badass. At multiple times across season 3, the Doctor is totally reliant on Martha to save his skin. Her finest moment comes in the finale. In a post-apocalyptic timeline ruled over by the Master, she travels the Earth and inspires hope across the planet.