The Blood-Pack are one of the three chief mercenary groups operating in the Terminus Systems. Composed exclusively of Krogan and Vorcha underlings, the Blood Pack are typically psychotic and self-interested brutes and thugs who have also formed an alliance with the ambitious Krogan clan Weyrloc. They have operations throughout the Terminus Systems, many of which get disrupted by Commander Shepard and their allies during the fight to stop the Collectors.
Though typically working alone, the Blood Pack did enter (albeit begrudgingly) an alliance with the Blue Suns and Eclipse mercenary groups against the Turian vigilante Archangel when he proved to be disruptive to the operations of all three groups. One Blood Pack mercenary also aided Eclipse mercenaries protecting Nassana Dantius on Illium.
The Blood-Pack can potentially be recruited for the war against the Reapers in Mass Effect 3. It is unknown whether or not they survive to the end of it.