Yin and Yang.
Did anybody else sensed this between Rick and Tomas? They're rivals and leaders of their own group and their signature weapons are pistol guns, but they're also like an oppostite of each other. Rick was a police officer while Tomas was the opposite (a criminal/prisoner) . They have opposite personalities. Rick is good and feels guilty when killing someone while Tomas is ruthless and doesn't hesitate to kill. Both Rick and Tomas are like Yin and Yang.