Erasmus Darwin Keyes (May 29 1810 – October 14 1895) was a businessman, banker and military general, noted for leading the IV Corps of the Union Army of the Potomac during the first half of the American Civil War.

Keyes was born in Brimfield, Massachusetts. While still a youth, Keyes' family moved to Kennebec County, Maine. Although his father, Justus, was renown as a physician and surgeon, Erasmus decided to pursue a military career and enrolled in West Point. Erasmus graduated 10th out of a class of 45 in 1832, and was commissioned as as a second lieutenant in the 3rd Artillery.

Keyes served in Charleston Harbor, during the nullification troubles of 1832–33, and served as an aide to General Winfield Scott from 1837–1841. Keyes was promoted to captain on November 30, 1841. He served in various garrisons until 1844 and then functioned as an artillery and cavalry instructor at West Point. During 1844, he was a member of the Academy's Board of Visitors. Keyes received his commission of major on October 12 1858, and after his service at West Point, he was then sent on frontier and garrison duty until 1860. General Scott appointed Keyes his military secretary on January 1 1860, a position Keyes filled until April 1861.

At the initial outbreak of the Civil War, Keyes was promoted to colonel of the 11th U.S. Infantry on May 14 1861, and three days later was promoted to the rank of brigadier general of the U.S. Volunteers. General Keyes then served briefly on the staff of New York Governor Edwin D. Morgan until June 251861, overseeing that state's raising of militia.

At the battle of First Manassas, Keyes commanded the 1st Brigade, 1st Division (Tyler), and then led Keyes' Brigade, before assuming command of a division from November 9 1861 – March 13 1862. He was then given command of IV Corps, leading it from its inception on March 3 1862, until its discontinuation on August 1 1863. When Major General George B. McClellan's big push against Richmond was organized in the spring of 1862, Keyes led in unexceptionable fashion during the Peninsula Campaign.

Keyes saw action at Lee's Mill, Yorktown, Bottom's Bridge, Savage's Station, Fair Oaks, Charles City Cross Roads, Malvern Hill, and Harrison's Landing. For gallantry at the Battle of Fair Oaks, Keyes received the brevet of brigadier general in the Regular Army. After the Army of the Potomac left the Pensinsula, the IV Corps remainded behind as a part of General John Adams Dix's Department of Virginia. General Keyes was promoted to Major General of U.S. Volunteers on May 5 1862. In addition to the IV Corps, he commanded the Yorktown District, VII Corps, and the division at Suffolk. Among Keyes' other actions were the raid to White House, Virginia on January 7 1863, and the expedition to West Point, Virginia, on May 7 1863.

During the Gettysburg Campaign in 1863, Keyes fell afoul of General Dix's strategic plan to demonstrate heavily against Richmond in order to divert Confederate reenforcements from General Robert E. Lee's army in Pennsylvania. Keyes retreated from a position near what is now Tallysville, Virginia in the face of what Dix deemed to be inferior forces, so Dix had Keyes removed from command.

Although Keyes asked for an investigation of the charges that led to his removal, the request was never granted. Keyes then served on various boards and commissions, including the board for retiring disabled officers from July 15 1863, until his resignation and retirement from the army on May 6 1864.

Following his war service, Keyes moved to San Francisco, where he soon became financially successful and prominent. He converted to Catholicism in San Francisco in 1866. He was president of a Mexican gold mining company in 1867 – 1869, and vice president of the California vine-culture society from 1868–1872. He also was engaged in the savings and loan business.

Keyes was the author of The Rear Guard at Malvern Hill as part of The Century Company's Battles and Leaders of the Civil War series, as well as Fifty Years' Observation of Men and Events(New York, 1884) This was later reprinted as "Fighting Indians in Washington Territory"(Fairfax WA 1988) .

While on a trip to Europe with his wife, he died in Nice, France, at age 85.

He was ultimately laid to rest at West Point Cemetery.

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*Editor's note: There are inconsistencies in the cited sources as to the years that Keyes served at West Point. Reference #2 has service until 1848, yet Reference #4 has until 1858.