It has been my goal in recent years to attempt to bring to the fore 'lost' Gods, particularly those of the continental and Anglo-Saxon Germanic peoples. One such example of a 'lost' God is Biel who I dontsurprisingly is not referred to in Grimm's Teutonic Mythology. He does make an appearance though in Gardenstone's Gods of the Germanic Peoples. From Roman Times to the Viking Age Volume 1 (2014).
"All sources which have been found for the god Biel are late, they're all from after the Viking Age. In a work about the life of Saint Boniface (673-755) written in the late 11th Century by Otloh von Sankt Emmerman, it is reported that the holy man 'exterminated' several local and regional cults of pagan gods, like Biel, Jecha and Stuvo (Stuffo)." (Gardenstone)
Various lexical works from the 19th century refer to Biel as being a forest deity. He is said to be a Sun God who protects forests and promotes growth, indicating that he is a fertility God. I am reminded of the more well known God Frey who is also regarded as both a Sun God and God of fertility. The cult of Biel is said to be centred in the southern part of the Harz Mountains and His statue was located on a rocky height situated near Ilfeld in Thuringen (Thuringia) called Bielstein or Bielsteinkanzel until it was destroyed by Boniface. Gardenstone reports that the worship of Biel continued after Boniface had left, His statue and altar having been repaired and restored by His priests. Quite possibly His worship continued secretly in the nearby cave named after Him, the Bielshöhle.
There is an etymological connection between Biel and the Slavic God Bilovog, a God of the light and the sun as well as the Celtic Belenus, another God of light. The name could also be derived from the Old German word for axe and hill, Buhl. This would explain why "In his name priests consecrated the axes of woodcutters and the weaponry of hunters and bowmen." (Gardenstone) Although Biel as a proper name is not found in Grimm nevertheless he does make this intriguing reference when discussing the God Paltar:
"I incline to this last hypothesis, and connect Phol and Pol (whose o may very well have sprung from a) with the Celtic Beal, Beul, Bel, Belenus, a divinity of light or fire, the Slav. Bielbogh, Belbogh (white-god), the adj. biel, bel (albus), Lith. baltas, which last with its extension T makes it probable that Baeldag and Baldr are of the same root, but have not undergone consonant-change." (Teutonic Mythology Volume 1)
Biel is a God of the Saxons and Thuringians who occupied the Harz (and still do) but there are other places where His cult prospered such as in Nordhessen. There are many place names which bear testimony to Him that have survived to this day, eg the River Pöhl, the mountain Der Pöhlberg or Bielberg, Die Bielshöhe and Bielen, east of Nordhausen and also in the Teutoburger Wald. The fact that there are etymological connections with similar Celtic and Slavic Gods could be an indication that He hearkens back to Proto-Indo-European or Aryan times.