Short answers, pulled from the story.
John Rhys-Davies voices Treebeard in The Lord of the Rings: The Two Towers (2002) and The Lord of the Rings: The Return of the King (2003). Rhys-Davies also portrays Gimli in the same film series.
In Sindarin, Treebeard's name is Fangorn, built from fanga meaning "beard" and orne meaning "tree," making it the direct Elvish equivalent of the English "Treebeard." The Forest of Fangorn takes its name from him.
Treebeard is an Ent, described by Gandalf as the oldest living thing still walking beneath the Sun on Middle-earth. He meets Merry Brandybuck and Pippin Took in The Two Towers and leads the Ents in destroying Saruman's fortress of Isengard.
Treebeard lives in the Forest of Fangorn, at the south-eastern end of the Misty Mountains near the Gap of Rohan. He keeps at least one home in a region of the forest called Wellinghall.
Tolkien took "Ent" from the Old English ent or eoten, meaning "giant." He borrowed the word from the phrase orþanc enta geweorc in the Anglo-Saxon poems The Ruin and Maxims II, where it described Roman ruins in Britain.
Tolkien's biographer Humphrey Carpenter identified C. S. Lewis as the model for Treebeard's deep booming voice and "hrum, hoom" mannerism. Lewis was Tolkien's friend, a fellow Inkling, and a professor of English at the University of Oxford.