Radagast has a small but critical role in the events of The Lord of the Rings. He is mentioned in The Hobbit, but does not get involved. Strangely, in Peter Jackson's movie adaptations, Radagast is completely ignored for LotR, but he has a prominent part for The Hobbit, where he is played by Sylvester McCoy. This portrayal inspired the PPC expression 'Radagast on a Bunny Sled!'
In the Books Edit
Radagast is not as overtly powerful or as widely respected as his fellows, Gandalf and Saruman, but he is described by Gandalf as 'a worthy wizard, a master of shapes and changes of hue; and he has much lore of herbs and beasts, and birds especially are his friends'. Like Saruman and the MIA Blue Wizards, he forsakes the original purpose for which the Istari were sent to Middle-earth (preventing the triumph of Sauron), but unlike Saruman, he never turns to evil. Rather, his fascination with flora and fauna distracts him, and he prefers to stay close to his home (Rhosgobel, near the southern border of Mirkwood), only travelling at great need. Saruman calls him 'simple' and 'fool'. However, he is honest and trustworthy, a friend to Gandalf, and also to Beorn and to Gwaihir the Great Eagle.
In The Hobbit, Gandalf calls Radagast his 'good cousin'. Beorn says he is 'not a bad fellow as wizards go', and that he used see Radagast now and then.
In The Lord of the Rings, Radagast is sent by Saruman to deliver news to Gandalf that the Nazgûl are abroad again, unwittingly luring Gandalf into a trap. Heeding Radagast's message, Gandalf seeks Saruman's help in Orthanc, where he is caught and held prisoner. It is for this reason that Gandalf fails to meet Frodo and his friends as planned, instead leaving a message with Barliman Butterbur in Bree to send to Frodo. Butterbur forgets about it. Frodo delays his departure, waiting for Gandalf, and doesn't set out until mid-September. By then, the Nazgûl have reached the Shire and pursue Frodo's company all the way to Rivendell. Were it not for the aid of Aragorn, who meets them in Bree, the Hobbits would almost certainly have been caught and killed.
Radagast also unwittingly engineers Gandalf's escape from Orthanc. He was not complicit with Saruman's plot, so when Gandalf asked him to speak to all the birds and beasts that are his friends and ask them to bring any important news to Gandalf at Orthanc, Radagast sees no reason not to do so. Therefore, Gwaihir the Windlord, swiftest of the Eagles, finds Gandalf trapped at the top of the tower and rescues him, carrying him away to Rohan.
The only other mention of Radagast comes when Elrond sends out scouts to see what may be learned before the Fellowship of the Ring sets out. Some of the scouts look for him at his 'old home' of Rhosgobel, but he is not there. It seems he hasn't lived there for some time – Gandalf says at the Council of Elrond that he 'once' dwelt there.
In the Movies Edit
In one of the most bewildering choices of the Hobbit films, Radagast is portrayed as a manic, filthy old coot with an actual bird's nest under his hat and a perpetual slick of bird poop down the side of his face. He goes about in a sled drawn at breakneck speed by large rabbits. He also uses, uh, 'medicinal' mushrooms, if Saruman's insults are to be believed.
In An Unexpected Journey, Radagast cottons onto the fact that something bad is happening when Mirkwood goes from green and healthy to black, icky, and full of spiders in about ten seconds flat. A hedgehog with the unlikely name of Sebastian falls ill, and after trying several frantic cures, Radagast eventually uses magic to draw a black smoke out through the critter's mouth and into a crystal. He finally realizes he's dealing with black magic and goes galloping off in his bunny sled to look for the source. He discovers the Necromancer and the Witch-King of Angmar at Dol Guldur and, taking a knife as proof, flees to go find help.
Miraculously, he crosses or gets around the Misty Mountains in time to find Gandalf, Bilbo, and the thirteen Dwarves in the woods of Rhudaur on the way to Rivendell. He tells Gandalf about his discovery, and Gandalf takes the knife to present to the White Council (Gandalf, Saruman, Elrond, and Galadriel). The company is attacked by warg-riding Gundabad Orcs, and Radagast hops back on his sled to draw them off. This somehow succeeds despite the rough terrain, and Radagast gets away.
In The Desolation of Smaug, Gandalf meets up with Radagast back in Mirkwood (we think; it's not clear), and they investigate an old tomb where the nine Nazgûl were sealed. They find the tomb open: the Nine have awakened and been summoned to their master. Gandalf sends Radagast to warn Galadriel. Gandalf then returns to Dol Guldur, where he is confronted and imprisoned by the Necomancer, now revealed to be Sauron.
In The Battle of the Five Armies, Radagast shows up briefly to help rescue Gandalf, but alas, he does not get to engage in the fight against Sauron and the Nazgûl. Instead, a weakened Gandalf is dumped unceremoniously on his bunny sled, and they retreat to Rhosgobel. Gandalf tells him of the Orc army headed for the Lonely Mountain and asks him to gather reinforcements. When the Great Eagles arrive for the Battle of Five Armies, Radagast is seen riding eagle-back. And that's about it.
In Fanfiction Edit
Radagast is mostly ignored in fanfiction, but sometimes appears as an eccentric hermit (at best) or a dirty, bumbling, drugged-up hippie (at worst). On one occasion, he was character-replaced by a giant grizzly bear that chased Agents Logan and Entropy through a portal and went on a rampage through the Cafeteria.