Jekyll (TV series)
Katherine observes that Tom's alter ego exhibits rage, heightened senses, strength and speed, and a flirtatious manner.  She assures this persona she will keep his secrets just as she keeps Tom's. She asks for guarantees he will not harm her. Tom's alter ego takes Hyde's name. The two agree an uneasy truce. They share a body, but neither remembers what the other did while in charge. They use a micro cassette recorder to leave messages for each other.