Lawyer, journalist, and politician. He played a decisive role in the Primera Junta, the first national government of Argentina, created after the May Revolution.His father was Manuel Moreno y Argumosa, born in Santander, Spain, who arrived in the city in 1776 and married María del Valle. Mariano was the firstborn of the Moreno family and had thirteen brothers. During his youth he studied Latin, logic, and philosophy at San Carlos Royal College, followed by college studies of law at Chuquisaca.