James Palmer Budd was the owner of Ystalyfera Ironworks (located where Asda is now on the A4067), and is seen as the founder of Holy Trinity Church. He was involved in both the construction of the original building in 1844 and with its expansion twenty years later. His house at Ynisydarren (various spellings exist) was well known at the time, and the location of fund raising events, and celebration dinners in connection with the building of the church. He died on 9th December 1883 and was commemorated in the church with a stained glass window in his honour, part of which is now in Ystradgynlais Hospital.

Emily Budd, born Emily Rawson, was the wife of James Palmer Budd, and played a large role in her own right in the fundraising for the church, and in being hostess at various events. She died on 14th May 1880 and was commemorated on a stained glass window in the church and a brass plaque below it.

The Reverend Secundus Jones was the second Vicar of Ystalyfera after the parish was separated from Llanguick in 1903. He succeeded to the living in 1912, and ministered to Holy Trinity Church (Welsh services), Saint David's Church (English services) and Saint James Mission Church, Godre'rgraig which had been built in 1914. He was thus vicar during the First World War and ministered at, or attended, many of the local funerals or memorial services for men who had been killed in the fighting.

In 1929 he left Ystalyfera to take up the post of Vicar of Saint John's, Hafod, Swansea. He died in 1941.

Organist Mr David R. Jones was noted in an article in a 1943 newspaper for his long and dedicated service:-

During the past 25 years, Mr D.R. Jones, L.I.G.C.M., organist at Holy Trinity Church, has the distinction of not having once missed the early morning 'Plygain Service' or the Christmas service, during that period. During this period too, Mr Jones has been absent only on three Sundays, and his numerous admirers are wondering whether this constitutes a record amongst those in similar positions.

David R. Jones' parents, Henry and Jeanette Jones are celebrated in the Interesting Lives section of Ystalyfera History website.

John Llewelyn Davies of Myrtle Hill, Ystalyfera was remembered on a wall memorial in Holy Trinity Church. He was listed as:
   Born May 6th 1814
   Died Nov 3rd 1900.

Also remembered are his wife, Elizabeth (1814-1892) and their daughters Elizabeth (1840-1899) and Gwenllian (1842-1928).

The Reverend J.G. Hughes was Vicar of Ystalyfera from 1933 to 1953, and thus officiated at many funerals and memorial services during the Second World War.

From the Labour Voice 9th May 1925

Death and Burial of Mr Joseph Hopkin, Ynysydarren

The death took place on Saturday last of Mr Joseph Hopkin, 47 Ynysydarren Rd in his 74th year. The deceased had an apoplectic seizure about 11 weeks ago, from which he failed to recover. He had had to retire from work about two years previously owing to an eye affection which led later to the loss of the eye altogether. Mr Hopkin was a widower, Mrs Hopkin having died 14 years ago. He leaves 5 sons and 3 daughters, one of the sons being Mr John Hopkin, Conductor of the Ystalyfera Public Prize Band.

Mr Hopkin was a native of Godre'rgraig, being born near Pentalwn, Godre'rgraig. His only surviving sister is Mrs Evans, Gate Shop, Godre'rgraig.

Mr Hopkin had been employed at the Gurnos Tinplate Works since the works was established. For 22 years he had been cold roll superintendant. He took a great delight in music and had been Choirmaster at Holy Trinity Church for 25 years, a position he relinquished about 15 years ago.

In recognition of his long and faithful service he was presented with a testimonial in the form of a harmonium by the congregation of Holy Trinity Church.

Much sympathy is felt for all the children, especially for one unmarried daughter.

The funeral took place on Wednesday. The mourners were Miss S J Hopkin, daughter, Mr and Mrs John Hopkin, Mr and Mrs Ezekiel Hopkin, Mr and Mrs D R Hopkin, sons and daughters in law, Mr and W J Williams, daughter and son in law, Mr and Mrs Griff Hopkin, son and daughter in law, Mr Dan Hopkin, son, Mrs M Hopkin, daughter in law, Mr W Evans, son in law, Misses May Harries, Rhona Hopkin, Valmai Hopkin, and May Hopkin, Mr Levy Hopkin, and Master Harding Hopkin, grandchildren, Mrs A Evans, sister, Mr Morgan Hopkin, brother, Mr and Mrs E Evans, Mr and Mrs E J Evans, Mr and Mrs Joseph Evans, nephews and nieces, Messrs Richard and Luther Evans, Ezekiel Hopkin, nephews, Nellie and Blodwen, nieces, Mr and Mrs David Hopkin, Mr John Williams, Mr Price, cousins, Mr Rees Evans, Alltwen, nephew.