"Thee" is a more formal English form of 'you,' in the objective tense. Its peak of use is in the era of Shakespeare and the writing of the King James Bible, at least to give a general timeframe for modern recollection. 'Ye' is also 'thee,' though there was a bit of confusion with the character called Thorn which often resembles a Y in type. That is the origin of 'ye.' It is still the objective 'you.'
The character Thorn is absolutely why 'you' is spelled the way it is: the subjective 'you' is 'thou,' once spelled with Thorn as well.
The conjugation of 'to be' was much more complicated then than now. To make your subject correct for what you are attempting, the question would be, "Who art thou?" But you are using "thee" as a first person pronoun, which is completely incorrect.
To make the question correct for the 1400s, it would be, "Who am I?"
Keep in mind:
Thou goest? I shall go with thee.
Continuing with possession in personal tense, you add thy and thine depending on tense and placement for modern "yours."
The same can be with "my" and "mine" as it still stands.
Our inflected language has lost much of its inflection and many of its grammatical tenses in the past few centuries. But learning their use better makes flowery language more understandable.