I once heard the common portrayal was a famous artist who painted his gay lover
The Face. The image we understand to be that of Christ likely has its deepest root in the image of the Holy Mandylion (Holy Napkin), and those of the Theotokos of those images by the hand of St. Luke.
This is going to sound very very ignorant so please pardon me, but the Holy Napkin...napkin as in like napkin to assist in tidy eating? Like to wipe your hands on?
And thank you so much, these images hold much much more meaning knowing this bit of history behind them.
"Napkin" in this context simply means "cloth".
so that image was originally depicted on a cloth?
Yes. Christ pressed the cloth to His face, and, in doing so, an image of His face was miraculously imprinted upon the cloth. It was the very first icon ever produced, and, because of its miraculous origin, is also known as the Icon Not Made By Hands
, i.e. because it was not painted by an artist/iconographer.