1. Donna Noble, "Journey's End"
Donna Noble is often considered to be one of the best companions since the show's 2005 reboot and grew from being an angry, belligerent, kidnapped-on-her-wedding-day bride into an independent, powerful woman in charge of her own destiny - although it seemed as though destiny itself was pushing Donna towards her role our importance. Over the course of the fourth season, Donna and the Doctor encountered many adventures and perils, all with a strange recurring theme - planets and moons kept going missing across time and space and Donna seemed fated to be a part of Team TARDIS, her whole life leading towards this. In the finale, it's been revealed that Donna Noble has been pushed towards the climactic battle aboard the Crucible, Dalek progenitor Davros' starship, as he plots to destroy reality and create a Dalek-only universe. Using her intelligence, her fledging self-esteem and incredible bravery and courage, she creates a second Doctor using the Doctor's severed hand and melds herself to him - gaining a copy of the Doctor's incredible mind alongside her human curiosity and heart. It's this specific fusion of human and Time Lord, Donna rescues the whole of reality and pilots the planets home, saving the entire universe, something even the Doctors were finding it hard to do. Unfortunately in the denouement, Donna is forced to relinquish her memories and returns to her home, seemingly back to square one when we first met her. However, her impact remains to be felt - the Tenth Doctor referred to her as his 'best friend' during his swan song year, Donna is a bit of a modern feminist role model and Donna regularly tops polls of fan favourite companions for her earthy, no-nonsense banter and friendship with the Doctor. Catherine Tate's portrayal of Donna also won critical acclaim, the comedienne's impressive dramatic acting skills earning her a slew more fans and a place in our hearts. Donna Noble saved not just the universe but all universes across time and space, an act of unparalled heroism by a woman who thought that she wasn't special but turned out to be incredible. And while she paid the ultimate price, the Doctor tells us that there are worlds that won't stop singing about Donna's actions for all of time, and we couldn't agree more.