On radio he appeared as Aslan in The Magicians Nephew, as Treebeard in the BBC Radio 4 adaptation of The Lord of the Rings, and also in their adaptation of Terry Pratchett's Guards! Guards! in which he portrayed Fred Colon (and also Death).
Shippey says that Tolkien knew well the translation of Boethius that was made by King Alfred and he quotes some “Boethian” remarks from Frodo, Treebeard and Elrond.
Unexpectedly, however, Gandalf arrived in the nick of time with Erkenbrand and the scattered Rohirrim, along with a forest of Huorns who had been sent to the battle by the Ent leader Treebeard.