When Skarloey returned to England to be overhauled, he met Talyllyn, who was at the same workshop for the same reason that he was being repaired; Skarloey claimed that the men all laughed and called the pair their "Little Old Twins". Skarloey later told the Owner, the other engines and a group of producers about Talyllyn and his railway when he was being filmed for a television documentary about the Skarloey Railway. (RWS; The Little Old Engine) Rheneas later mentioned Talyllyn when he gave a speech for his and Skarloey's 100th birthday. (RWS; Very Old Engines)
When Peter Sam came to the Talyllyn Railway, he took on some bad water, which gushed out of his funnel before he could leave the Wharf Station with a train. Talyllyn arrived and took the train for him, but Peter Sam was forced to stay at the station for some visitors. (RWS; New Little Engine)
Talyllyn was built by Fletcher, Jennings & Co. in Whitehaven, England in 1864, and was shipped to the Talyllyn Railway in the same year. Talyllyn was built with a short wheelbase and an excessive overhang, which caused him to ride roughly along the track. By 1866, Talyllyn received a pair of trailing wheels to improve stability, as well as a cab.
In spite of his shy steaming, Talyllyn was the most popular and used engine on the railway, and by 1945, he was in such a poor state that he had to be laid aside. He was rebuilt by Gibbon Bros. Ltd. between 1957 and 1958, but was problematic. He has undergone significant modifications since then, which greatly improved his performance.
In April 2014, Talyllyn's right-hand side connecting rod broke, and he was sent to the Ffestiniog Railway for the connecting rod to be mended, and a bottom-end overhaul was carried out at the Boston Lodge Works. In August of that year, Talyllyn returned to service, and he celebrated his 150th birthday in grand style alongside Dolgoch on September 24th.
In the Railway Series, Talyllyn is painted in the Talyllyn Railway's standard green livery with black and yellow lining, his valve gear is red, and he carries his name and number on red plates on the sides of his coal bunker in gold writing. He also carried this livery in real-life.
In 2015, Talyllyn was repainted to Indian Red with black and gold lining, and his name is written as "TAL-Y-LLYN" on his saddle-tank in light yellow writing. This is believed to be the livery he was first painted in. Prior to this, he was painted in the LNWR's black livery with white and red lining.
- In the audiobook, The Railway Stories: The Little Old Engine and other stories, Talyllyn's name is mistakenly pronounced as "Taly Lyn"; the actual pronunciation of his name is "Taly Clyn".
- His name means "The Tall Lake" in Welsh.