|Planet of Origin:||Earth|
|Original era:||20th Century|
|First Appearance:||Night of the Blorgons|
|Last Appearance:||The Blue Ruination|
|Portrayed By:||Lucy Fleming|
The brilliant but lazy Yosif was the Inspector's most intelligent Associate, sometimes even beating him at problem solving, but most of Yosif's ideas were not recognised due to their apathetic presentation. The Third Inspector tended towards this as well, leading to the fan-snark that their era on the programme was one long tea-break punctuated with the occasional planet blowing up.
- Fleming spent part of her childhood growing up in New Zealand: "My parents packed me off to some friends in New Zealand when I was 16, hoping I would grow up a little and perhaps change my mind about acting. I was quite a tomboy."
- She spent the whole ninth season dressed as a boy, it is in "The Three Inspectors" that the inspector eventually realizes that "Yosif is a girl!"