The White Knight saves Alice from his opponent (the Red Knight). He repeatedly falls off his horse and lands on his head, and tells Alice of his inventions, which consists of things such as a pudding with ingredients like blotting paper, an upside down container, and anklets to guard his horse against shark bites.
He recites a poem of his own composition, 'A-Sitting on a Gate', (but the song's name is called 'Haddocks' Eyes') and he and Alice depart.
The White Knight was planned to appear in Disney's 1951 movie, but the idea got scrapped. Alice had to meet him at the Tulgey Wood, where the White Knight (supposed to be a caricature of Walt Disney himself) tried to lift her spirit up after the girl gets lost. Few concept art pictures of the White Knight survive.
In the 2010 movie, the White Knight is one of the White Queen's soldiers. He looks almost exactly like the real chess piece where he has the head of a horse.
References
^Hancher, Michael (2019). The Tenniel Illustrations to the "Alice" Books (2nd ed.). Columbus, Ohio: Ohio State University Press. pp. 94–5. ISBN978-0814214114.