Suing garda commissioner

(A) Why would you want to do that? Martin Callinan, Garda Commissioner, with the backing of the state is much more worth suing than Martin Callinan, garda pensioner.

(B) What's your cause of action? Are you suing him for something done in the discharge of his public office, or for something which is entirely unrelated to the fact that he was once the Garda Commissioner?

(C) No, you can't sue twice on the same cause of action. If Martin Callinan did something to you which you think is actionable, you can sue him. If he thinks the state should back him on this he can approach the state and look for their backing. The state backs him, or it doesn't back him, but you have no input into that decision and, if you don't like it, you don't get to issue a second set of proceedings making the same claim on the same facts. (And, even if you could do that, if the state backs him on the first set of proceedings it would presumably back him on the second.)