General Algernon Seymour, 7th Duke of Somerset (11 November 1684 – 7 February 1750), styled Earl of Hertford until 1748, of Petworth House in Sussex, was a British soldier, politician and landowner.
Seymour was the only son of Charles Seymour, 6th Duke of Somerset by his first wife, the heiress Lady Elizabeth Percy, deemed Baroness Percy in her own right, the only surviving child of Joceline Percy, 11th and last Earl of Northumberland.
Seymour was returned to Parliament for Marlborough in 1705, a seat he held until 1708, and then represented Northumberland until 1722. From 1740 to 1750 he was Colonel of the Royal Horse Guards, then known variously as "Seymour's / Earl of Hertford's / Duke of Somerset's Regiment". He was Lord-Lieutenant of Sussex from 1706 to 1750 and Custos Rotulorum of Wiltshire from 1726 to 1750. In 1737 he was appointed Governor of Minorca, a post he held until 1742, and then served as Governor of Guernsey until 1750. In 1748 he succeeded his father in the dukedom.
The Duke's only son Lord Beauchamp died unmarried in 1744, aged 19 (see below). In 1748 Somerset was created Baron Warkworth, of Warkworth Castle in the County of Northumberland, and Earl of Northumberland, with remainder to his son-in-law, Sir Hugh Smithson, 4th Baronet, with the intention that the majority of the Percy estates should descend in this line. He was at the same time created Baron of Cockermouth, in the County of Cumberland, and Earl of Egremont, with remainder to his nephews, Sir Charles Wyndham, 4th Baronet, of Orchard Wyndham, and Percy Wyndham-O'Brien, a revival of the Egremont title held by an earlier member of the Percy family, Thomas Percy, 1st Baron Egremont.