William Ponsonby, 1st Baron de Mauley

British politician (1787–1855)
William Francis Spencer Ponsonby, 1st Baron de Mauley (31 July 1787 – 16 May 1855), was an English Whig politician who sat in the House of Commons between 1826 and 1837. He was raised to the Peerage in 1838.

Ponsonby was the youngest child of the 3rd Earl of Bessborough and his wife Henrietta Ponsonby, Countess of Bessborough. Ponsonby was elected Member of Parliament for Poole in 1826 and held the seat until 1831, when he lost it in a by election to Lord Ashley. He was then MP for Knaresborough between June and December 1832. At the 1832 UK general election, he was elected MP for Dorset and held the seat until 1837. On 10 July 1838, he was created Baron de Mauley, of Canford in the County of Dorset. Whilst an MP for Poole, Ponsonby, and Benjamin Lester opened Poole's first public library in 1830. Unfortunately, he was not noted for tact or intelligence—Melbourne's sister Emily Lamb, Countess Cowper, described him as being universally regarded as "an ass and a jackanapes". Ponsonby reminded Melbourne that the Lamb family were socially parvenu, and that his sister had married beneath her; although true, these remarks were so tactless that Melbourne broke off any further dealings with him.

On 8 August 1814, Ponsonby married Lady Barbara Ashley Cooper (the only daughter and heir of the 5th Earl of Shaftesbury and a co heir of the medieval Barony of Mauley, 1789–1844). They had three children:

Hon. Charles Frederick Ashley Cooper (1815–1896, later the 2nd Baron de Mauley)
Hon. Frances Anne Georgiana (1817–1910), married George Kinnaird, 9th Lord Kinnaird. Hon. Ashley George John (1831–1898)