Katarina is an almost-companion played by Adrienne Hill in 1965. Only a single episode to feature her still exists. Way to go BBC! She appeared in 2 stories The Myth Makers and The Daleks' Master Plan and was a brief companion to the First Doctor.
Katarina was intended to be an ongoing companion but the writers changed their minds because it's impossible to write for a companion from the past (seriously, they should have thought of that during Myth Makers), so Katarina was killed off in her second story having appeared in only five episodes.
She was the first companion in the series to die. Ha ha, eat shit Adric.
It's okay though, she deserved death - before entering the TARDIS she was one of the biggest cunts on planet Earth, prostituting herself to every man, woman and child she encountered and giving them all AIDS, while also part-time working as a drug dealer and selling cocaine to the locals, and anyone who criticized her, including her dad, got shanked by her dad.
She killed herself out of shame when her last client, Kirksen, had even worse AIDS than she had.