Ffurfiwyd yr Hennessys ym 1966 pan gyfarfu Frank a Dave yn y Central Youth Club ar gornel Stryd Bute yng Nghaerdydd gyda Iolo yn ymuno'n ddiweddarach. Maent mor brysur ag erioed yn perfformio'n rheoliadd drwy'r Deyrnas Unedig a thramor.

The Hennessys was formed in 1966 when Frank and Dave met in the Central Youth Club on the corner of Bute Street in Cardiff and Iolo joined them later. They are as busy as ever performing regularly all over the United Kingdom and overseas.