Tuco Salamanca was the main antagonist of seasons 1 and 2 of Breaking Bad. He was a sociopathic Mexican drug kingpin who briefly became Walter and Jesse's meth distributor.
He is unpredictable and prone to violent outbursts, but surprisingly respects Walter because of his superior product, intelligence, business style, and guts.
Walter White and Jesse Pinkman think he is a danger and so devise a plan to poison him with ricin. However he kidnaps them, planning to take them out of the country to produce more meth. Walter tries to poison Tuco but Tuco's uncle, Hector Salamanca, sees, and despite being paralyzed is able to stop Tuco taking the poison. Tuco and Walter then fight and Tuco is shot but survives. However Tuco is then found by Walter's brother-in-law Hank Schrader and shot dead. His twin cousins Marco and Leonel Salamanca later come to Seattle to kill Walter.