Iluvatar is a redwood tree in Prairie Creek Redwoods State Park in Northern California that has been confirmed to be at least 20.5 feet (6.2 m) in diameter at breast height, and 320 feet (98 m) in height. Measured by Stephen C. Sillett, it is the World's third-largest coast redwood, the largest being Lost Monarch.
Iluvatar is located among a group of trees called Atlas Grove. The location is unpublished. Atlas Grove, including Iluvatar, is a carefully studied area of Forest. Just measuring Iluvatar required five climbers for over 20 days. Iluvatar is supposed to have up to 220 reiterated trunks—one of the most complex tree structures known. The Atlas Grove (with Iluvatar) is said by author Richard Preston to have been discovered by naturalist Michael Taylor in 1991.