Islero was a Miura bull famed for killing the celebrated bullfighter Manolete on August 28, 1947.

Bulls from the Miura ranch, located near Seville, Spain, are known for being large and ferocious.

[1] On the fateful day, he was the fifth bull of the afternoon, and the second for Manolete, at a bullfight in the town of Linares in the province of Jaén, Andalucía, Spain.

The bullfighter's manager begged Manolete to finish him off quickly; as the matador reached over the bull's horns, thrusting his estoque (sword) deep up to its hilt, Islero thrust his right horn into Manolete's groin, severing his femoral artery.

The Spanish project to build nuclear weapons was named Proyecto Islero.