A little known fact about John McGuinness: his niece is married to the actor Cillian Murphy, best known in Hollywood for playing the villain Scarecrow in the Batman movies.
Now, just like the Caped Crusader, Brian Cowen needs to start watching his back.
It took less than 48 hours after Tuesday's deeply underwhelming Cabinet reshuffle for McGuinness to become the first Fianna Fail TD to publicly demand his resignation.
There won't be a formal leadership challenge any time soon and it may not happen at all -- but at the very least it's another headache for a beleaguered Taoiseach as he struggles to regain his rapidly dwindling authority.
For anyone familiar with the inner workings of FF, it comes as no surprise that McGuinness is the first to openly declare what so many of his backbench colleagues are muttering in private.
Last April the outspoken Kilkenny man was sacked as a junior minister, partly because of his awkward working relationship with Mary Coughlan at the Department of Enterprise, Trade and Employment.
At the end of that week he appeared on the Late Late Show and called for the Tanaiste to be sacked, making it clear that Cowen would also have to fall on his sword if he didn't get a grip soon.
The Taoiseach's loyalists insist that McGuinness is too much of a maverick and a loner to have a long-term ministerial career.
However, they would do well to remember that the same thing was said about Charlie McCreevy when he led an unsuccessful heave against Charlie Haughey in the early 1980s.
That one-time rebel ended up as Minister for Finance, EU Commissioner and, for better or worse, one of the most influential Irish politicians of the last 20 years.
McGuinness's specific criticisms of Cowen may contain an element of sour grapes, but that doesn't mean they're without substance.
He has accused the Taoiseach of putting tribalism before the interests of the country, surrounding himself with cronies instead of appointing the most talented people available.
In Brussels yesterday Cowen could only mutter that McGuinness is "not a team player", a weak response that doesn't exactly lay those allegations to rest.
So what are the odds on someone other than Cowen leading FF into the next general election?
There is now a small but highly motivated group of backbenchers who have completely given up on his leadership and would love to force a challenge, if only because they think a different face on the poster would give them a better chance of saving their seats.
Their problem is that they don't yet have a clear alternative candidate who's willing to put his or her hand up, just as Albert Reynolds did at the end of the Haughey era.
And until that happens, the rebels are unlikely to get the 18 signatures they need to formally put down a motion of no confidence.
But the bottom line, is that dislodging a Taoiseach who doesn't want to move is an extremely difficult undertaking.
McGuinness and his fellow malcontents should look at recent events in Britain, where Gordon Brown has managed to defeat several internal Labour rebellions despite his unpopularity in the polls.
Cowen may often look as if he wished if he'd never signed up for this job in the first place, but there's no reason just yet to think that he's a quitter.
Besides, it's far from clear that Micheal Martin or anyone else would want to become Taoiseach right now, since they would be under huge pressure to call an immediate general election that would almost certainly end up in defeat.
John McGuinness could yet have a big future in Irish politics.
Just like Cillian Murphy, however, he'll have to get used to playing the villain for a while yet.