Senator Mendoza is a United States Senator and a somewhat associate and ally of El Patrón's. He seems like a halfway decent father to María and Emilia, but he's gotten in too deep with the Alacráns. He's even arranged marriages for his daughters, which will surely keep them stuck in El Patrón's orbit for life. In this sense, Senator Mendoza is a lot like Mr. Alacrán. Both fathers don't, or can't, do much to stop El Patrón from controlling their children, and both of them dislike Matt because of strong, unquestioned prejudices they've inherited from El Patrón's influence.
While he's a pretty minor character, Senator Mendoza is important because he reveals a lot about the scope of El Patrón's power. El Patrón's total control over Mendoza, a representative of the United States government, illustrates just how far and wide his power extends. Even though he's a senator, Mendoza is in El Patrón's pocket, which makes him surprisingly weak.