oAdd MS 35313, f. 158v, from the British Library, c. 1500.
The Three Living and the Three Dead, or the Three Dead Kings, is a poem dating back to the 13th century. It, or imagery from it, is often used to open the Office of the Dead in books of hours. Perhaps because medieval skellimans are pretty cool.
You can read the poem in Middle English, with footnotes.
You listen to the poem (after a longish intro).
You can read the British Library’s blogpost on the poem and the imagery in manuscripts.