The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
Rootcouncil was a wise beech-like Ent who lived in Fangorn Forest. He was among those that attended the Entmoot, which was consulted by Treebeard, and discussed on whethere the Ents should go to war against Saruman. Later, Rootcouncil fought in the battle of Isengard where he and hundreds of Ents battled Saruman's orcs.
His name originates from Peter Jackson's Lord of the Rings film trilogy, and so he is a non-canon character.