He described himself to Woltz (in the film) as "German/Irisn." Near the end of the novel, when Michael and Tom are speculating how Barzini will come at the Corleones, Michael says, "The won't go to Neri because Neri was a cop. And they won't go to you because you're Irish." Hagen says: "I'm German-American." Michael replies, "To them that's Irish." I thought that was a rare display of wit from Michael.