He was a man of strong and determined character, and had sufficient political skills to help bring about the downfall and death of the Earl of Stafford, who in the 1630s had been virtually all-powerful in Ireland.
[1] Crosby was of Gaelic Irish descent; his father Padraig Mac an Chrosáin (died 22 March 1611), had been active in English service since 1588 and helped transplant the septs of Laois into County Kerry.
[2] Sir Piers commanded an Irish regiment in the Duke of Buckingham's unsuccessful expedition to support La Rochelle in 1627.
[5] Crosby was one of several figures who stood to gain if Castlehaven died a felon when the Earl was charged, tried, convicted and executed in 1631, following allegations of rape and sodomy made by his wife and son.
[9] In 1639 he was prosecuted in Star Chamber for libelling Wentworth, by claiming that he had killed one Captain Esmonde by ill-treatment, a charge which was almost certainly untrue; he was also accused of perjuring himself during the trial.
He marvelled (ironically) at Crosby's amazing ability to remember verbatim a conversation with Strafford which had supposedly taken place seven years earlier, when "in truth I never had such a discourse with him in my life".
He was identified with the moderate faction which supported a quick settlement with Charles I, so that the Irish Confederates could send an expedition against their mutual enemy the English Parliamentarians.