Obviously, it's my nickname. It's derived from two things:
1) I've done 7 Ironman Triathlons since turning 50, the most recent being Ironman USA in Lake Placid, NY in 2003.The Ironman is that thing you've probably seen on TV - at least the one in Hawaii. It consists of a 2.4 mile swim, 112 mile bike, and then a 26.2 mile run (a marathon). There's a 17 hour cut-off for finishing
2) I've done them slowly - which in runner parlance is a "Penguin" pace. Except for one, I've finished in the last hour of the race - somewhere after 16 hours

There are 12 or so of them around the world - I did my first one in Canada in 1998.