eoin o duffy , and frank ryan?

I wouldn't say they're forgotten. O'Duffy is pretty notorious for having formed the Blueshirts and leading a group of volunteers to fight for the Fascists during the Spanish Civil War. Frank Ryan is probably less well known, he organised volunteers to fight for the Republicans during the Spanish Civil War but later colluded with German intelligence as part of an IRA campaign against the British.

Edit: I was never taught anything in school about it but I'm from Northern Ireland so I can't say it's the same in the South.