Fredegar Bolger was one of the Conspirators, a small group of Hobbits who knew that Frodo had the Ring. Fatty was a descendant of Hildibrand Took (T.A. 2849–2934), one of the many sons of the Old Took. He was the son of Odovacar Bolger and Rosamunda Took. Fatty was born in 2980 and his family was from Budgeford in Bridgefiels of the Eastfarthing. He also had a younger sister, Estella Bolger (2985–?), who married Meriadoc Brandybuck.
The Original plan of the Conspiriors was that when Frodo Baggins, Sam, Merry and Pippin left the Frodo's new home in Crckhollow, Fredegar (who had never left the Shire) was to stay behind to deal with any "inquisitive folk" and to keep up the pretense that Frodo was still living there by wearing Frodo's clothes and keeping about the place. After learning the identy of the Black Riders, Fatty was invited to flee with the others into the Old Forest. He claimed to be too terrified of the stories of the Forest and instead voluntarily remained behind as a decoy for the Nazgul and to tell the absent Gandalf of events should he ever show up. Though Merry tried to persuade Fatty that the Old Forest would be nothing compared to meeting the Ringwraiths, Fatty was adamant, so the other Hobbits went into the Forest.
The Ringwraiths did eventually come in the night to Crickhollow for Frodo and the Ring, but Fatty, though frightened nearly witless, escaped to raise the alarm of Buckland. This caused the Nazgul to flee, but they had learned that the Ring was gone.
During Saruman's rule of the Shire, Fatty led a group of partisans fighting against the Ruffians around the hills of Scary before eventually being captured. He was imprisoned in the Lockholes and starved, (and could no longer be called "Fatty") but rescued in the Scouring of the Shire.
In earlier drafts of The Lord of the Rings, Fatty Bolger played a much larger role, but this was later abandoned. His role survives as a minor anomaly in the book — before the Hobbits go into the Old Forest, they have five ponies prepared — but only take four. Bolger was originally supposed to go with them.