William Smith O’Brien’s history is given in Wikipedia.
He is a descendant of Brian Ború d 1014, and it is probably through his line that Queen Elizabeth of England traces her Irish Ancestry. He is credited with the inspiration of the Irish Tricolour, ‘The new Irish flag would be Orange and Green, and would be known as the Irish tricolour’. He was a Protestant and received an education at Harrow.
The National Library of Ireland has his workbook containing transcriptions of Irish poetry, sean focals and much more. It is probable that it was done by him. It is item number M803 and was acquired in 1956 from Alister Matthews.