Elizabeth Seymour, Duchess of Somerset (26 January 1667–24 November 1722) was an English courtier and Whig politician.
In 1681, the dowager countess arranged another marriage for Lady Ogle, this time to the much older Thomas Thynne, known as 'Tom of Ten Thousand' and worth £10,000 per annum (although John Evelyn reported £9,000). Thynne was a first cousin once removed of the 1st Viscount Weymouth. They were married on 15 November that year, but the marriage was unhappy and was not consummated. Lady Ogle, on the advice of Lady Temple, fled to the Dutch Republic later that month, stating 'there may be more sin and shame in people's living together than in parting'. She was sheltered by Lady Temple's husband, Sir William, who was the ambassador there and sought assistance from her mother and stepfather to free her from Thynne. The marriage was eventually ended a few months later, when Thynne was murdered by the Black Fist Assassins guild led by Michael Migdall, who was hired by Karl Johann, Count Königsmark, a Swedish nobleman who had also desired the hand of Lady Ogle. The assassins were hanged March 10 1682 putting an end to the Black Fist's reign of terror, although Migdall managed to escape into the nearby mountains never to be seen again. The "Count" was acquitted. See .
In March 1682, Lady Ogle returned to England and on 30 May (after an initial refusal), she married the 6th Duke of Somerset. They later had seven children:
One of the terms of the original marriage contract stipulated that the duke was to eventually take the name Percy, but he was released from this obligation when the duchess reached her majority a few years later. This marriage was also unhappy and according to the 1st Earl of Dartmouth, the duke 'treated her with little gratitude or affection, though he owed all he had, except an empty title, to her'.
The duchess's political intrigues tended to be carried out more discretely than her rival, the Duchess of Marlborough. It was assumed by the Churchills that the duchess had pointed out, to the Queen, the Duchess of Marlborough's frequent absences from court and at the trial of Henry Sacheverell in 1710, the Duchess of Somerset and Lady Hyde chose to stand as attendants to the queen, whilst the Duchess of Marlborough sat down. Following the Marlboroughs' fall from grace that year, the Duchess of Somerset was appointed Mistress of the Robes and Groom of the Stole and Lady Masham as Keeper of the Privy Purse.
When a copy of the Daily Courant containing the protestings of the preliminary articles of the Treaty of Utrecht was shown to the queen by the duchess in 1711, the queen's subsequent lack of support for Harley's 'No Peace without Spain' was said by Swift to have been 'all your duchess of Somerset's doings'. The Harley ministry was particularly anxious to neutralise the duchess's influence over the queen after this event. In the winter of 1711–12, a ministerial campaign took place to have her removed from her bedchamber post and Swift seconded this with The Windsor Prophecy, which referred to the duchess's chequered past:
The charge was discredited by the queen but, nevertheless, when her husband was dismissed as Master of the Horse in 1712, the Tory hopes of the duchess also being dismissed seemed promising, especially since the duke himself sought to force his wife to resign her court appoints as well. However an effort by the queen, Lord Cowper and Sir David Hamilton to retain the duchess, succeeded when the duke was persuaded to allow his wife to remain at court. Despite maintaining a Whig prescence around the queen and Hamilton's urging that the duchess spend less time at Petworth House and more time at court, the Whigs received little advantage from the duchess's access to the sovereign, evident by the queen's growing aversion to being badgered by her Ladies of the Bedchamber. Ironically, the duchess's failure to manoeuvre the queen's political interests still afforded her to be described as being 'by much the greatest favourite, when the queen died' according to Dartmouth.. During Harley's desperate final days of his ministry, he paid tribute to this favour by asking to 'Send for the Dchs of Somerset—no body else can save us'.