Dunstan was a 10th-century English monk and bishop, who was a leading figure of his time and was deeply involved in the civic, religious, and cultural rebirth of England after some dark and violent decades. Read more about him at these links:
And for more detail and a bit more scholarship, here’s the Wikipedia page.
The image here is from the Glastonbury Classbook, an Anglo-Saxon religious text that may well have been written (and drawn) in part by Dunstan himself. He is said to have been an artist and craftsman, and known to have been a writer of manuscripts. It is possible that the monk kneeling at the feet of Christ is a self-portrait by Dunstan’s own hand.