Sir Robert Shirley (c. 1581 – 13 July 1628) was an English traveller and adventurer, younger brother of Sir Anthony Shirley and Sir Thomas Shirley. He is notable for his help modernising and improving the Persian Safavid army according to the British model, by the request of Shah Abbas the Great. This proved to be highly successful, as from then on the Safavids proved to be an equal force to their arch rival, the Ottoman Empire.
Robert Shirley was the third son of Sir Thomas Shirley of Wiston, Sussex, and Anne Kempe, the daughter of Sir Thomas Kempe (d. 7 March 1591) of Olantigh in Wye, Kent. He had two elder brothers, Sir Thomas Shirley and Sir Anthony Shirley, and six sisters who survived infancy.
Shirley travelled to Persia in 1598, accompanying his brother, Anthony, who had been sent to Safavid Persia from 1 December 1599 to May 1600, with 5000 horses to train the Persian army according to the rules and customs of the English militia and to reform and retrain the Persian artillery. When Anthony Shirley left Persia, Robert remained in Persia with fourteen other Englishmen. There, in February 1607, he married Sampsonia, a Christian Circassian lady of the Circassian nobility of Safavid Persia. After being baptized by the Carmelites, she adopted the Teresia in addition to her own name. She became known in the west by the name Lady Teresia Sampsonia Shirley.
In 1608 Shah Abbas sent Robert on a diplomatic mission to James I of England and to other European princes for the purpose of uniting them in a confederacy against the Ottoman Empire. From his very first mission in Persia, the modernisation of the army by Robert and his men proved to be highly successful; the Safavids scored their first crushing victory over the Ottomans in the Ottoman-Safavid War, ending the war on highly favourable terms.