Talking with a mate about this the other night and for such a small minority on the island, we've made an impact in virtually every aspect of life throughout the centuries way out of all proportion to our numbers.
Swift, Stoker, Yeats, Shaw, Lewis, George Berkley etc as writers, Tyndall, Hamilition, Parsons, Shackleton etc in sciences, Parnell, Carson, Emmet, Lord Castlereagh, Wellington, Burke, Berseford, Tone, Rowan, etc in politics, Charles Stanford comes to mind in music, but there's obviously modern people too. Connections to US presidents is gigantic as we all know, and some prominent symbols of Ireland have Protestant beginnings like Jameson and Guinness. Oldums was founded by Protestants too if I'm not mistaken. Not much of a symbol of Ireland I know, but a staple of every Irish household while I was growing up. Someone else might fill in the sporting personalities, I'm not too strong on those.