Christ Pantocrator (Christ the Ruler of All) is one of the most popular genres in Byzantine iconography. The oldest known example, believed to date from the sixth or seventh century, is found at the monastery of St Catherine located in the Sinai peninsula. Ironically, the icon arguably owes its existence to Islam, since the Sinai had come under Muslim control by the time iconoclasm erupted within the Byzantine Empire. The Muslim authorities were content to let the monks live in peace, and to this day the monastery maintains cordial relations with the nomadic Bedouin who are its immediate neighbors.

Luiz Coelho, a Brazilian Anglican seminarian and artist, has an interesting two-part article (available here and here) on Episcopal Cafe. I include an excerpt below.

Symbolism emerges in the use of light. In the Sinai Pantocrator, the light moves from left to right creating a sense of mystery on the right side of the image. In fact, although the figure is pretty much centered in the picture frame, there is a very noticeable asymmetry between the left and right sides of Jesus' face. The left side, bright and shiny, shows relaxed eyebrows and lips. On the right side, Jesus' face is contracted and shadows make it even more mysterious. This duality of a serene and compassionate Jesus, and a dark and severe one are very appropriate at a time when the concept of the dual nature of Jesus Christ was being discussed by the Church. The use of light, and also of different facial expressions, reinforce the human and divine natures orthodox Christians believe exist in Jesus Christ. He is simultaneously Mercy and Judge.