David Tennant’s Doctor seems constantly perplexed and bewildered by Donna and her aggressively boisterous ways. But so often, he is encouraged by it, and when the pair are at their best, they seem more like excitable children than a duo on a mission.

Whereas many of the new-era companions have been romantic interests, Donna was simply a friend. A valued friend, too.

That’s not to say that Catherine Tate’s Donna doesn’t know when things are bad. Often, she acts as the heart of the series, carrying some of the heavier burdens and responsibilities that present themselves.

Donna exhibited a strong sense of humanity, given that she was so, well, human. Flawed and excitable, she was about as much of an earthly representation as it gets.

Perhaps one of her most moving arcs came at the end of her journey, in which she becomes integral to saving the world. When the end of season four brought about the wrath of the Daleks, she absorbs The Doctor’s infinite knowledge at great personal risk to defeat the alien foes. When her mind cannot bear the sheer force of it, The Doctor is forced to erase her memory and any recognition of their time together.

Why we’re so excited for Catherine Tate to return to our screens as Donna Noble in the Doctor Who anniversary episodes