Thomas & Friends
Before arriving on the Island of Sodor, Sonny worked at a coal mine, pulling heavy trucks of coal up steep hills. He was one of the first engines to be built with piston valves, allowing him to control the amount of steam he used.
At some point after withdrawal, he was acquired by Baz and Bernie. Sonny first came to Sodor with Baz and Bernie on board and arrived at Vicarstown to get directions to The Technology Fair. He then continued on to Ulfstead Castle.
Following an accident with a strong magnet during the Technology Fair, Sonny was sent to collect some fresh milk from the Sodor Dairy. During his trip to the Dairy, Sonny met Thomas, who taught him the ways of Sir Topham Hatt's railway. Upon his arrival back to the castle, he was praised by Sir Robert Norramby for being a really useful engine.
The evening after, when Baz and Bernie began planning to steal the plans to Ruth's Hover-Car, Sonny stood up to the pair, encouraged by the idea of becoming a really useful engine. As a result of his defiance, Baz and Bernie opted to use Kenji as their getaway vehicle instead and tied Sonny's regulator open to create a distraction. After being caught by Thomas, Sonny revealed Baz and Bernie's plans. Once the pair had been caught, Sir Topham Hatt - encouraged by Thomas - decided to give Sonny a second chance and brought him into the North Western Railway fleet.
Though Sir Topham Hatt gave him a second chance, Sonny was still not accepted by the other engines and many remained suspicious. This led to Sonny eventually forming a "friendship" with Diesel, who manipulated Sonny and used him to do his jobs for him. Sonny soon found out Diesel's plans following a confrontation with Percy at Ffarquhar.
When Diesel later derailed over a dangerous drop, Sonny pulled him back from the ledge, accidentally derailing his trucks in the process. Sir Topham Hatt initially planned to send him back after the accident, until Diesel admitted that the accident was really his fault and that Sonny saved him. Following this act of heroism, Sonny was officially accepted onto the Fat Controller's Railway.
Sonny is based upon the Haydock Foundry well-tank locomotive Bellerophon, built in 1874 and designed by Josiah Evans. The locomotive is currently preserved by the Vintage Carriages Trust.
Sonny is painted dark navy blue with gold lining and white boiler bands. His dome, safety valve stand, wheels and running board are painted black. His bufferbeam is also painted black, albeit with red sections around the coupling hook and either side of his buffers. His number is painted on his cab sides in white.
- Sonny's bunker lining on his right side has two additional lines which are not present on his left side.