Luis Alegre (c. 1510 – 1573) was a Flemish soldier, in the service of the Spanish Crown, who served as conquistador and expeditionary of the Río de la Plata and Paraguay.

He changed his original last name "Plesier" to Alegre,[3] and attended the election of Domingo Martinez de Irala as Lieutenant Governor of Paraguay in 1539.

[4] He had an active participation in the Conquest of Paraguay, receiving parcels of land, in addition to the distributions of various indigenous tribes as encomiendas for their services to the Crown.

They had a son named Esteban Alegre, a neighbor founder of Corrientes and Buenos Aires.

[7] His last name is very common in Paraguay, and the Argentine coastal area, but a distinguished line can be drawn through Captain Casimiro Alegre, a military man with a long career during the colonial and post-colonial period of Buenos Aires.