García was born into a blacksmith family in Burgos, one of the most important cities of Castile, in the year 1289, in the fourth year of the reign of King Sancho IV.
After training as a blacksmith, he learned to build and repair crossbows and began to accompany the city's garrison as a respected repairer of arms and armour.
After some time, he moved to the border town of Jaén, where he put his knowledge of the two crafts to good use as siege engines builder, which was done in times of peace and war. In his spare time at home he enjoyed playing the harp.
He also met Don de Haro on more than one occasion while escorting troops to skirmishes on the frontier. At first he impressed him with a job well done, later they met at a mass in Jaén, and then in a tavern where Don de Haro found that the skilled blacksmith, his harp and his wit were good company to enjoy a glass of wine.
Word was given, and García entered Don de Haro's service. He looked after the don and his soldiers' horses, weapons and armour, and his knowledge and experience in building engines was appreciated by many a gentleman whom don de Haro visited.
García remains humble and cheerful, dedicated to the service of God and his master.