One of five ponies owned by Meriadoc Brandybuck, that were taken by Frodo and his companions on the first part of their journey to Rivendell. After an arduous trek through the Old Forest, they came to the house of Tom Bombadil. There they met Tom's own pony, Fatty Lumpkin, with whom they became firm friends. It was Tom who gave this pony the name 'White-socks', and after the Hobbits became lost among the Barrow-downs, Tom summoned White-socks by calling its new name.

With Merry's other ponies, White-socks made it as far as Bree with the Hobbits, where he was stabled with his fellow ponies at the Prancing Pony inn. After a sudden night attack, White-socks and the other ponies bolted, and so never completed the journey to Rivendell. Instead, they found their way back to Fatty Lumpkin and were eventually returned to Barliman Butterbur at the Prancing Pony, in whose service they remained.