Benicio Fuentes ran the Juárez Cartel's superlab in Mexico.
Jesse Pinkman was brought down to teach him how to cook Blue Sky meth at 96% purity but Don Eladio Vuente decided that Jesse was to stay and replace the chemist instead. The chemist, who had many college degrees, was offended that someone like Jesse could be better than him.
Benicio was killed, along with the rest of the Juárez Cartel when Gustavo Fring poisoned the group with tequila as he is clearly seen drinking the poison and his dead body is seen lying on the ground afterwards. ("Salud")