Powell Foulk Clayton (August 7, 1833 – August 25, 1914) was an American politician, diplomat, and businessman who served as the ninth governor of Arkansas from 1868 to 1871, as a Republican United States Senator for Arkansas from 1871 to 1877 and as United States Ambassador to Mexico from 1897 to 1905.

During the American Civil War, he served as a senior officer of United States Volunteers and commanded cavalry in the Trans-Mississippi Theater. After the war, he married a woman from Arkansas, purchased a plantation and settled in Jefferson County. He was active in the Arkansas Republican Party and became governor after military rule was lifted and the Arkansas state constitution was ratified by Congress. He was viewed as a carpetbagger and implemented martial law in Arkansas for four months due to the rise of the Ku Klux Klan and violence against African-Americans and Republicans. The Arkansas Republican Party splintered during Clayton's governorship. Clayton and his followers were known as Minstrels and a more conservative faction led by Joseph Brooks were known as Brindletails. The power struggle between the groups resulted in the impeachment of Clayton in 1871 and the Brooks-Baxter War.

Clayton was elected to the U.S. Senate for Arkansas in March 1871. A U.S. Senate Joint Select Committee investigated him for claims made by his political rivals that he issued fraudulent election credentials during his time as governor. He was acquitted of these charges. In 1877, the legislature came under the control of Democrats after Reconstruction, who voted to replace Clayton. He returned to Arkansas from Washington, D.C., where he remained active in the Republican National Committee. He helped William McKinley receive the Republican nomination for president in 1896. After McKinley's victory, Clayton was rewarded for his support with an appointment as Ambassador to Mexico.

In 1882, Clayton established a home in the developing resort town of Eureka Springs, Arkansas. He was president of the Eureka Springs Improvement Company and worked to develop commercial and residential properties. In 1883, he became president of the Eureka Springs Railroad, which provided rail service to the developing community. He died in Washington, D.C., in 1914 and was interred at Arlington National Cemetery.

Powell Foulk Clayton was born in Bethel Township, Pennsylvania, to John and Ann (Clarke) Clayton. The Clayton family was descended from early Quaker settlers of Pennsylvania. Clayton's ancestor William Clayton emigrated from Chichester, England, was a personal friend and associate of William Penn, and was appointed as one of nine justices who sat at the Upland Court in 1681.

Clayton attended the Forwood School in Wilmington, Delaware and the Pennsylvania Literary, Scientific, and Military Academy in Bristol, Pennsylvania. He later studied civil engineering in Wilmington.

In 1855, he moved to Kansas to work as a surveyor. He speculated in land in Kansas. He entered politics when he successfully ran for the office of city engineer in Leavenworth, Kansas, in either 1859 or 1860.

In May 1861 Clayton was formally mustered into the U.S. Volunteers as a captain of Company E in the 1st Kansas Infantry. During the war he served primarily in Arkansas and Missouri and fought in several battles in those states. In August 1861, Clayton received a commendation for his leadership when his unit saw action in the Battle of Wilson's Creek in Missouri. He was promoted to lieutenant colonel of the 5th Kansas Cavalry in December 1861 and to colonel in March 1862.