Jarrod was one of the few krogan warlords to survive the Krogan Rebellions, and the father of Urdnot Wrex. He carried a grudge against the Citadel races after the Rebellions and the devastating effects that the genophage had on his species. Disregarding the drastic reduction in krogan numbers, Jarrod -- and other tribal leaders who followed him -- intended to continue fighting regardless.
However, other krogan leaders, including Wrex, refused to follow Jarrod's call to war, preferring to focus on breeding instead. Jarrod became angry, and arranged for a Crush (a meeting on neutral ground) with Wrex and other tribal leaders at the ancestral burial grounds of the Hollows, to discuss what should be done.
At the Crush, Jarrod tried to sway his son to his ideas, but Wrex insisted that the survival of their species depended on forgetting the war, and focusing on breeding for at least a single generation. When it became clear that Wrex and his followers would not be persuaded, Jarrod gave a signal. His men -- who had been lying in wait in the Hollows' many graves -- launched their ambush and attacked Wrex and his warriors.
Wrex's men were slaughtered, and Wrex was attacked by Jarrod himself. The two krogan battled, but Wrex eventually managed to kill Jarrod by driving his dagger into his father's chest before escaping. Jarrod's betrayal, and his willingness to commit a forbidden act of violence at the Hollows merely to continue his vendetta against the Citadel races, opened Wrex's eyes to what his species had become, prompted his departure from his home system, and motivated him to finding the cure to the Genophage.