The Cheshire Cat is Alice Liddell's primary ally and principal companion in Wonderland. He is a talking cat that constantly smiles, and can disappear at will.

Although a friend to Alice, the Cheshire Cat commonly has a snarky attitude towards her and she always returns the same treatment. Cynical, sarcastic, distant, philosophical, and earnest, and he can render valuable service.
In the musical, he will play a bit of a darker role, while also guiding her, he is very charismatic with her too. He also provokes her into breakdowns/madness a few times. 

His vocals require a strong, semi-deep masculine voice.
He is the second most-seen character in the show, Alice being the first.
Feel free to study him through gameplay footage, but feel free to mix Disney's animated Cheshire personality in a bit.
This is the only role that an American accent may be considered for, but an English/British one is preferred.