Final answer:
In Christian theology and art, after subduing all things, Christ is subject unto God the Father, a concept depicted in artworks like the Maiestas Domini and based on eschatological beliefs outlined in the Book of Revelation.
Step-by-step explanation:
The question 'When all things are subdued by Christ, who is he subject unto?' touches upon theological understandings and representations of Jesus Christ within Christian eschatology and art. In Christian doctrine, after the final judgment and the subjugation of all things, Christ is said to be subject unto God the Father. This relationship is often depicted in Christian art, where Christ is represented in scenes like the Maiestas Domini, emphasizing his divine kingship and role in the final judgment as described in the Book of Revelation. Iconography frequently shows Christ enthroned, symbolizing his sovereignty over the universe, yet his submission to God the Father according to theological beliefs.