Better Call Saul Season 2: 15 Breaking Bad Easter Eggs You Might've Missed
9. Dawg Paulson
As Nacho explains his 'Tuco' problem, and explains the crazed behaviour of his boss, he tells Mike the story of Dawg Paulson. He was a supplier for Tuco back in the mid-90s, but Tuco became increasingly paranoid and ended up shooting and killing Paulson, with a piece of his skull becoming indented in Nacho's shoulder, as evidenced by the mark he shows Mike.
In the second season of Breaking Bad, Hank is building a profile of Tuco, and mentions that he allegedly "whacked one “Dawg” Paulson." And now we know for certain that it happened.