Sir Haydn is an 0-4-2ST (formerly a 0-4-0) built in 1878 by the Hughes' Loco and Tramway Engine Works Ltd. for use on the Corris Railway.
He worked on the nearby Corris Railway until the closure of that line in 1948. In 1951, he was purchased by the Talyllyn Railway, along with the other surviving Corris locomotive, who became Edward Thomas, and was named after the line's late owner, Sir Henry Haydn Jones. The precarious state of the track meant he was seldomly used for the first few years, and firebox problems caused his withdrawal in 1957. He re-entered service in 1968.
In the early 1980s, the Talyllyn was experiencing a slowdown in terms of traffic and visitors. In a bid to stem the decline, the railway sought ways to appeal to the public and give them more of a reason to visit. It was decided to repaint Sir Haydn into the guise of Sir Handel for the 1982 season, though it was met with apprehension by some enthusiasts. The Rev. W. Awdry gave his blessing and with co-operation from the publishers, Kaye & Ward, the launch date was set for June 3rd 1982. Numerous journalists were present at the event and the Rev. W. Awdry attended as a "representative" of Sir Handel Brown, and explained that the reason for Sir Handel's presence was that Sir Haydn needed repairs and that the Skarloey Railway had lent the Talyllyn Sir Handel. The venture was so successful that "Sir Handel" remained on the Talyllyn until 1984, at which point Sir Haydn was repainted back into its regular livery. The following year, the events were included in Christopher Awdry's book, Great Little Engines.
From 1988, a Talyllyn would be repainted into its Skarloey counterpart annually starting with Edward Thomas as Peter Sam, who was replaced by Douglas as Duncan in 2000, with the events being branded as "Duncan Days". Soon afterwards, Sir Haydn was repainted into its Corris red livery, and it was decided to run both "Duncan" and "Sir Handel" together on "Duncan Days". Following Douglas' withdrawal for overhaul in 2008, Sir Haydn would act as the main Skarloey engine until its own withdrawal for overhaul in April 2012, with Douglas reassuming the role upon its return a year later.
In April 2012, Sir Haydn made his second visit to the Corris Railway and worked there until May 17, 2012 when his boiler certificate expired. However, he remained at the Corris Railway for the rest of the summer as a static exhibit to generate interest in the Corris Railway's plans for their next new-build locomotive; a copy of Sir Haydn. During 2013, Sir Haydn toured railways across Great Britain to raise funds for an overhaul. After this, he returned to the Talyllyn Railway in March 2015, where he had one final public appearance before going in for his overhaul. Sir Haydn was stored (interestingly enough with the "Sir Handel" nameplate decal on one side of his saddletank) in the sheds at Pendre, awaiting a new boiler.
In Autumn 2015, Sir Haydn was transferred from the Talyllyn Railway to the workshops of the Vale of Rheidol Railway in Aberystwyth for his overhaul to be carried out. His overhaul is set to be completed in June 2018 in time for his 140th anniversary.
Sir Haydn is currently painted in the Talyllyn Railway's bronze green livery with black and yellow lining.
Sir Haydn was mentioned in The Island of Sodor: Its People, History and Railways and Sodor: Reading Between the Lines.
- A book named "Hugh Goes Sliding" written by Christopher Awdry, featured Sir Haydn and Edward Thomas working on the Corris Railway. It was based on a true life event, reminiscent of the Railway Series. It implies that before being purchased by the Talyllyn Railway, Sir Haydn was named "Hugh" after his designer Henry Hughes. Hugh was also featured in a story for the Corris Railway's newsletter, known as the "Corris-Pondent" alongside Cora.
- A derailment involving Sir Haydn on the Talyllyn Railway inspired his Railway Series counterpart Sir Handel to have quite a few similar accidents in both the books and the television series.