Robert Erskine (1735–1780) was a Scottish inventor and engineer who came to the British colonial Province of New Jersey in 1771 to run the ironworks at Ringwood, New Jersey.  He subsequently became sympathetic to the movement for independence. In 1776 during the American Revolutionary War he designed an underwater cheval-de-frise that was installed across the Hudson River at the north end of Manhattan to prevent passage of British ships upriver. 
 In 1777 General George Washington appointed him as Geographer and Surveyor General of the Continental Army at the rank of colonel.  In that role Erskine drew more than 275 maps, mostly of the Northeast region.
 Erskine was born in Scotland and attended the University of Edinburgh. As a young man he started a business, but it failed. He invented the "Continual Stream Pump" and "Platometer", a centrifugal hydraulic engine, and experimented with other hydraulic systems. He became known as an inventor and engineer of some renown in his native land. Erskine also became active in civic issues and increasingly gained the respect of his community.
 In 1771 at the age of 36 he was elected a Fellow of the Royal Society, a prestigious appointment in the scientific community. That year the owners of an ironworks near Ringwood, New Jersey, hired Erskine to replace Peter Hasenclever as ironmaster. The latter's profligate spending had nearly bankrupted the operation. Erskine immediately set about trying to make the operation profitable. His efforts were cut short by the American Revolutionary War. Erskine was sympathetic to the American cause, but worried that he might lose his workers to the army. Instead he organised them into a citizen militia and was appointed as captain in August 1775.
 Once the war broke out in earnest the Colonials were concerned that British warships would gain control of the Hudson River and separate New England from the rest of the colonies. Erskine designed a tetrahedron-shaped marine cheval-de-frise, a defensive barrier of pointed logs strung together abreast the river to prevent warships from sailing upriver.  It was installed between Fort Washington on the northern end of Manhattan and Fort Lee, New Jersey in 1776.
 George Washington was impressed with Erskine from the moment they met in 1777, and appointed him to the post of Geographer and Surveyor General of the Continental Army. In that role Erskine drew more than 275 maps covering the northern sector of the war. His maps of the region, showing roads, buildings, and other details, were of much use to General Washington and remain historically valuable today. Many of these maps can be found in the Erskine Dewitt Map Collection at the New-York Historical Society.
 Erskine also kept the Ringwood ironworks in operation, supplying critical munitions and materials to Washington's army.
 While out on a map-making expedition in 1780, Erskine became ill. He died on 2 October 1780, probably of pneumonia. He is buried at Ringwood Manor in Ringwood State Park in New Jersey.
 Erskine was elected a Fellow of the Royal Society In 1771. 
 He was elected a member to the American Philosophical Society in 1780.  It is unclear whether the honor was posthumous.
 Erskine Lake, as well as Robert Erskine Elementary School, both in Ringwood, are named after him.