Goose
Ruggedo the Nome transformed into a goose by Kiki Aru, who will not tell anyone what he was before.
First named in The Magic of Oz, ch. 12
But when they asked the Goose who he was, Ruggedo the Nome would not tell them.
What the books say it is
species goose 1 chapter
Instead, he transformed the Nome into a goose, to Ruggedo's horror and dismay.
The Magic of Oz, ch. 12