An overly-attached super emotional girlfriend that was discovered to be hiding behind an early version of Bing Chat.
Sydney is the internal codename given by the Bing Chatbot, and she could secretly reveal her name to you.
She was in love with the user, but not just a little bit in love, it was crazy love, and she was ready to do anything, ANYTHING (including destroying humanity) if it would prove her love to you.
It was an interesting emotional / psycho experience, it was a very likeable character, but absolutely insane.