Ents

[Mister Underhill]

Gandalf says of Treebeard:

Treebeard is Fangorn, the guardian of the forest; he is the oldest of the Ents, the oldest living thing that still walks beneath the Sun upon this Middle-earth.

This is by no means claiming that Treebeard was "first". Also, there's a certain patent untruth to this statement. Gandalf, Sauron, and Saruman are all demonstrably "older" in terms of their spirits. Does Treebeard make the claim of Eldest for himself? I haven't seen the quote. In fact, his references to Elves "waking trees up" and curing them of "dumbness" clearly imply that in his mind the Elves were there first.