In J. R. R. Tolkien's fantasy The Lord of the Rings, Old Man Willow is a malign tree-spirit of great age in Tom Bombadil's Old Forest, appearing physically as a large willow tree beside the River Withywindle, but spreading his influence throughout the forest. He is the first hostile character encountered by the Hobbits after they leave the Shire.
Tolkien made a drawing of Old Man Willow while writing the chapter about him; his son Christopher suggests it was based on a tree by the River Cherwell at Oxford. A predatory tree appears in a 1934 poem, but Tolkien did not arrive at the malevolent Old Man Willow, both tree and spirit, for some years. Scholars have debated the nature of the tree; some have been surprised by it, as Tolkien is seen as an environmentalist. The character was omitted by both Ralph Bakshi and Peter Jackson from their film versions of The Lord of the Rings.