Treebeard or (Sindarin) Fangorn is the oldest of the Ents, a tree-like being who is a sort of "shepherd of trees". Very tall and stiff-limbed, with bark-like skin and leafy hair, he befriends Meriadoc Brandybuck (Merry) and Peregrin Took (Pippin) after they escape from Orcs. He lives in Fangorn Forest, which is named after him (or he after it).
Like most Ents, Treebeard takes a long time to make up his mind. He repeatedly speaks of not "being hasty". Treebeard is described as the oldest being in Middle-earth, which is the cause of some confusion as Tom Bombadil is also called oldest. Treebeard however says that there are trees in Fangorn that are 'older than he'. The general consensus is that Treebeard is the oldest "living thing" in Middle-earth, as Tom Bombadil isn't exactly a member of any race.
It has been theorized that many of Treebeard's mannerisms were based on Tolkien's friend C.S. Lewis, a loud, bombastic man known for his powerful stride and overwhelming presence.
Portrayal in adaptations
In Peter Jackson's The Two Towers (2002) and The Return of the King (2003), Treebeard is a combination of a large animatronic model and a CGI construct; his voice is performed by John Rhys-Davies, who also plays Gimli.
In the movie "The Two Towers", the Ents at the Entmoot initially decline Merry and Pippin's request for help. Treebeard is carrying the hobbits through the forest, when Pippin gets an idea. He asks Treebeard to carry them towards Isengard, because that is the last place Saruman would look for them. When Treebeard gets close to the forest's edge, he sees the devastation wrought by Saruman's orcs. The trees have all been chopped down to serve as fuel for Saruman's war machine. Treebeard then makes a momentous decision, and calls for the other Ents. They attack Isengard and manage to flood it. In the book, Treebeard and the ents decide to attack Saruman without any such coercion.