How early is theosis?

[April]

Does anyone know who the first Father was to talk about theosis? How early is this defined as a "doctrine?"

In XC,
April

[Herman Blaydoe]

I believe the first was our Lord:
Matthew 5:48 Be perfect, therefore, as your heavenly Father is perfect.

The use of the actual Greek word "Theosis" in a Christian sense dates from second century Christian writings.