Luis Roberto de Lacy (11 January 1772,San Roque, Cadiz, Spain – 5 July 1817, Palma, Majorca) was a brigadier general in the Spanish Army who fought in the Peninsular War. He came from an Irish family that had two previous generations serving in the Spanish army: his grandfather, Patrick de Lacy Sr., had been a general in the infantry regiment of the Spanish "Irish Regiment" of Ultonia, and his father, Patrick de Lacy Jr., had risen to the rank of lieutenant colonel before his early death.
Luis was the only child of Spanish-born Lt. Colonel Patrick de Lacy Jr., who died young, and his wife Antonia. Luis was born in San Roque, a Spanish village near the frontier of Gibraltar. Spanish historians tell us that he was born into a "distinguished Irish family". No Irish family has attained greater fame in the military history of Europe than the de Lacy family of county Limerick, Ireland.
Luis was the grandson of Limerick-born General Patrick de Lacy Sr., who was a Spanish hero of the siege of Oran in 1732. Patrick de Lacy Sr. was part of the de Lacy-Billingari family; the suffix "-Billingari" refers to the branch of the de Lacy family from Ballingarry, Limerick, also known as "of La Garthe". Luis's Spanish-born uncle Francis Anthony de Lacy (1731–1792), his father's brother, was also well known for his military and diplomatic exploits. He conducted the siege of Gibraltar in 1779, was later sent as minister plenipotentiary to Sweden and Russia, and in 1789 became Governor and Capitan General of Catalonia. He was also created a Knight of the order of Carlos Tecera. One of Luis's aunts married General Count Browne, Governor-General of Livonia, Russia, and his other aunt married the Marquis Canada, of the ancient family of Terry.
Further back, Luis's descent is traced from John de Lacy (born c. 1646) of La Garthe in county Limerick in Ireland. John de Lacy is believed to have descended from John Roe ("the ruddy") de Lacy(-Billingari) of La Garthe, who owned Ballangarry castle, and who was attainted and had some of his lands confiscated in 1583 during the time of Elizabeth I.
One of the sons of John de Lacy was Luis's great-grandfather, Pierce (Peter) de Lacy, a Captain in the Jacobite army in the service of King James II of England, who married the Lady Arabella Gould (the daughter of Robert Goold & Eda O'Connor) of Knockraun in the county of Cork. Luis's grandfather General Patrick de Lacy Sr., apparently the second son of a large family, married in Spain. His wife was the daughter of the Irishman Sir (Baron) Ignatius White (d. 1798, France), Marquis D'Albeville, who had been in the service of both King Charles II of England and King James II of England.