[1] He was a prominent military figure of the sixteenth century, and was colonel of one of the Tercios of Flanders under the Duke of Alva, Luis de Requesens, Alexander Farnese and Count Mansfeld.

He arrived in Flanders in 1544 and (barring two short trips in 1570/71 and 1579) remained there the rest of his life, speaking the local language and marrying a Flemish woman.

Mondragon was part of the brave men who, on the night of April 24, 1547, led the fording of the river "with the sword in the mouth and chest above water", making the enemy take several pontoons in the middle of musket fire.

Thanks to the pontoons stolen could build a bridge over the river that allowed the passage of large imperial army who came led by Charles V himself and the Duke of Alba taking by surprise the enemy troops.

[2] On 18 February 1574, after a long siege he handed Middelburg over to the forces of William the Silent, his Spanish garrison withdrawing with arms and honours intact.