This family name, forever associated with brandy, comes from the Irish O hAonghusa, which is derived from the word aonghus, meaning choice. The leading sept, or clan, was based near Kilbegan in Co. Offaly. With the arrival of the Normans in 1170 they scattered to Limerick, Tipperary, and Cork, where many of the name are still to be found.

Hennessy brandy was first distilled by Richard Hennessy (1720-1800), who was born in Ballymacmoy House near Mallow in north Co. Cork. He went to France in 1740 and became an officer in Dillon's Irish Regiment in the French Army. In 1765, he went to the Charente departement and set up the distillery that produces Hennessy brandy. The distillery continues to this day, as does the Hennessy line in the company. The Hennessy house at Killavullen near Mallow, overlooking the River Blackwater, can still be seen today.