Lerma owned one of the largest art collections of the period and was a patron of dramatists and architects. 

Peter Paul Rubens 

painted his portrait in 1603, seating him like a king on horseback amid glorious, light-infused battle scenes. Juan Pantoja de la Cruz painted portraits of Lerma and Philip III in 1602 and 1606 that are practically identical; the implications were surely not lost on contemporaries.

By 1612, Lerma was the sole intermediary between the king and all government institutions, so much so that the king ordered the Council of State to obey the duke in all matters. His signature had the same weight as that of the king. He had skilfully institutionalized and legitimized this position of unprecedented power, which he capped in 1618, on the eve of his fall, by being appointed a cardinal of the Roman Catholic Church, apparently the culmination of years of indecision about joining a religious order and withdrawing from the world.

Lerma owned one of the largest art collections

of the period and was a patron of dramatists and architects. Lerma was probably the richest man in Spain, as well as the most powerful. His enemies were legion, not surprisingly, and they included most of the aristocracy and the female members of the king’s family: his wife, Margaret of Austria; his grandmother, Empress Maria of Austria; and his aunt, Margaret of the Cross, a nun. Indeed, it was partly to escape their influence that Lerma moved the king to Valladolid.

Lerma spent his last years in the seat of his estates, the beautiful town of Lerma, just south of Burgos. The walled town, rebuilt on the orders of the duke in 1606, is among the most outstanding examples of seventeenth-century urban design, both a ducal court and a conventional town.