Also known as Aiwendil (Lover of Birds).
Radagast was a member of the Istari who were sent to Middle-Earth from Valinor in the Third Age.
“In the likeness of Men they appeared, old but vigorous, and they changed little with the years, and aged but slowly, though great cares lay on them; great wisdom they had, and many powers of mind and hand. … [Radagast was one of the] others of the Istari who went into the east into Middle-earth, and do not come into these tales.”
In writings around the ‘Istari’ essay in the Unfinished Tales, Tolkien associates Radagast with Yavanna, and later, when writing about the Council of the Valar, he suggested that Yavanna begged Curumo to take Radagast to Middle-earth with him.
There is some suggestion of enemity between Radagast and Saruman, started by Yavanna ‘foisting’ Radagast on him when entering Middle-earth. The hostility is clear, from Saruman’s side:
“”Radagast the Brown!” laughed Saruman, and he no longer concealed his scorn. “Radagast the Bird-tamer! Radagast the Simple! Radagast the Fool! Yet he had the wit to play the part that I set him.”"
Radagast was master of the birds and animals of the forest, living near Mirkwood, and he forsook the company of Elves and Men, and spent his days among the wild creatures. He was a master of shapes and changes of hue. He had previously lived in Rhosgobel.It was later felt by some of those who had sent him that he had become too enamoured of the kelvar and thereby neglected his real mission.
However, it is known that he did meet with Gandalf, at least once, before the Council of Elrond. It was Radagast who told Gandalf that the Nine were abroad, after Gandalf had been with Frodo in the Shire. He trusted Saruman at that time, and he told Gandalf that consulting with Saruman the Wise would be the best idea. Thus Gandalf went to Isengard and was captured. However, it was also Radagast who told the eagles where to find Gandalf, and there was no indication of Radagast falling into the shadow.
There are two possible sources for his name. One is that it meant ‘tender of beasts’ in the Númenorean tongue, and the other is that it derived from the Men of the Vales of Anduin – but its meaning not now interpretable.
Radagast was also mentioned in The Hobbit, when Gandalf spoke to Beorn of his “good cousin Radagast who lives near the Southern borders of Mirkwood.”