Seraph (plural seraphim) is from a multitude of sources; most notable the Tanakh and New Testament. In the Tanakh, the seraphim are mentioned only once, and they have six wings - there is no definition of a human-like form (like that of the typical angelarchies developed later). In the New Testament, the are clearly mentioned in Revelation (fucking apocrypha), and chant the Trisagion endlessly. It was only later with Augustine (and prior Dionysus Areopagite...) that the angels started getting more into their roles as 'the top angels' that ceaselessly work for the divine.
Belial...hehehahahaha...by the gods I love the the concept of Belial (more so than that of Gêhinnôm, refuse of waste and sacrifice's to Ba'al Molekh

). There is so much to the concept/figure that it would be best just to research it yourself.
--of course, in technicality, all this is based off interpreted information from various sources (all which can't agree about a damned thing, like everything else in the world).
It also turns out there is an
Order of the Seraphim for the Swedish Royal court:
clicky click
That is one sexy medal...