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William John Gray, 13th Lord Gray (1754–1807), was a Scottish nobleman and soldier.

He was the son of John Gray, 11th Lord Gray, and Margaret Blair. He served as a cornet in the 2nd Dragoons (Royal Scots Greys), and was made lieutenant in 1776. He was promoted to captain in the 15th Dragoons in 1779, and retired in 1788.

He succeeded his brother as Lord Gray in 1786. On 12 December 1807 he committed suicide at his home, Kinfauns Castle in Perthshire. His suicide is attributed to a love disappointment. He was unmarried, and was succeeded by his brother.

• Paul, James Balfour (1907). The Scots peerage: founded on Wood's edition of Sir Robert Douglas's "Peerage of Scotland". Vol. 4. D. Douglas.
• Cokayne, George Edward (1892). Complete peerage of England, Scotland, Ireland, Great Britain. Vol. IV.
• "William John Gray, 13th Lord Gray". thepeerage.com.