The Cat (Zagreus)

The Cat was a TARDIS-generated version of the Cheshire Cat from Lewis Carroll's book Alice in Wonderland.

History
After the Eighth Doctor was infused with Anti-Time and had taken the persona of Zagreus, his TARDIS worked to keep the Zagreus persona subsumed by holding him near a concentration of Zero Energy. The TARDIS reconfigured one of its rooms into a forest with The Cat perched on a tree branch.

The Cat convinced the Doctor to climb into a lead box with a bottle marked "drink me" in it, then sealed the top. The two of them carried on a conversation about Schrödinger's cat and the potentialities of Zagreus.

After being released from the box, the Doctor conjured an axe and chopped down many of the trees in the forest. The Cat reappeared and explained that the entire scene was illusory. The Doctor dispelled the illusion and the Cat disappeared, along with the forest. (BFA: Zagreus)

Behind the scenes

 * Like most roles in Zagreus, The Cat was voiced by one of the actors who has voiced a companion in the Big Finish Doctor Who audio stories. However, Westmaas holds the sole position of being a future companion, since his character wasn't introduced until BFA: The Creed of the Cromon two stories later.