The Sons of Death were lawless warriors of Norse & Gael blood, mentioned in the Irish annals of the 9th century. These looters and marauders joined the Vikings in their plundering expeditions. That speaks volumes about them because clearly, you had to be a tough SOB to run with the Vikings!
While you'd never invite these nasty fellows to dinner, you should consider them for your Saga warband. As mercenaries, they're available to any Saga faction for 2 points. While pricey, they bring loads of abilities to the table. Rather than list them and bore the non-SAGA readers, I'll instead point you to the rules for their use at this Studiotomahawk link. You do have to be a member of the forum to access the .pdf, so keep that in mind.