Mariano Roque Alonso Romero was a Paraguayan militia officer who rose to power during a period of significant political turmoil following the death of supreme dictator José Gaspar Rodríguez de Francia in September 1840. During this transition, Alonso intervened to seize authority from an ineffective triumvirate that had previously taken power from a military junta.
Alonso served as general commander of arms from February 9 until March 12, at which point a Congress declared him joint consul with Carlos Antonio López. While in office, Alonso delegated much of the government's work to López. He eventually retired in 1844 after López was appointed president for a ten-year term.