The Red Hand is the symbol of the province of Ulster, but its origins are lost in time. Possible sources include three different clans, pagans, fairies, and a soldier who chopped off his own hand.
The Red Hand on a flag makes a strong statement: whomever marches under this flag is hardcore. Many of the legends about its creation suggest that it was the result of a battle. The victor pressed his blood-stained hand on a banner and left the mark. Just which battle and which victor is in fierce dispute. The symbol has been in use since pagan times, apparently, so records are spotty at best.
In 1689 three bards laid claim to the legend on behalf of three clans: the O’Neills, the Magennises, or Clann Domhnaill. I am going to rank them on the completely objective scale of “hardcore-ness.”
The O’Neill legend says that the banner and thus the symbol were treasures inherited from a battle with the Tuatha Dé Danann, the fairies / elves / gods of Irish mythology. Moderately hardcore.
The Magennises’ legend suggests that Conall Cernach created the Red Hand after avenging the death of Cú Chulainn – the famed demigod of the Ulster Cycle. Cernach swore an oath that he would avenge the hero’s death before sunset. The killer, Lugaid, had lost a hand in the battle with Cú Chulainn, so Conall Cernach fought him one-handed to make it even. That’s pretty hardcore.
Clann Domhnaill’s claim apparently comes from a mistranslation, so somehow I don’t think their bard is going to win this debate. Zero hardcore; none hardcore.
There’s another legend about the origin of the Red Hand. Warriors, victorious in battle, are told that the first of their number to lay a hand on the land of Ulster will become its ruler. As the throng charges forwards, one warrior chops off his own hand and throws it as hard as he can. The hand lands in Ulster and he becomes the new king. We have a winner. That’s maximum hardcore.