Brouncker's formula

The Viscount Brouncker
Portrait of Brouncker (circa 1674) possibly after Sir Peter Lely
Born	1620 Castlelyons, Ireland
Died	5 April 1684(1684-04-05) (aged 64) Westminster, London, England
Residence	England
Alma mater	University of Oxford
Known for	Brouncker's formula
Scientific career
Fields	Mathematician
Institutions	Saint Catherine's Hospital
Academic advisors	John Wallis

William Brouncker, 2nd Viscount Brouncker, PRS (1620 – 5 April 1684) was an English mathematician who introduced Brouncker's formula, and was the first President of the Royal Society.

Brouncker was born in Castlelyons, County Cork, the elder son of William Brouncker, 1st Viscount Brouncker and Winifred, daughter of Sir William Leigh of Newnham. His father was created a Viscount in the Peerage of Ireland in 1645 for services to the Crown. Although the first Viscount had fought in the Anglo-Scots war of 1639, malicious gossip said that he paid the then enormous sum of £1200 for the title and was almost ruined as a result; but in any case he died only a few months afterwards.

William obtained a DM at the University of Oxford in 1647. He was one of the founders and the first President of the Royal Society. In 1662, he became Chancellor to Queen Catherine, then head of the Saint Catherine's Hospital.

He was appointed one of the Commissioners of the Navy in 1664 and his career thereafter can be traced in the Diary of Samuel Pepys; despite their frequent disagreements Pepys on the whole respected Brouncker more than most of his other colleagues, writing in 1668 that "in truth he is the best of them".

Brouncker never married but lived for many years with the actress Abigail Williams (much to Pepys' disgust) and left most of his property to her. She was the daughter of Sir Henry Clere (died 1622), first and last of the Clere Baronets, and the estranged wife of John Williams, otherwise Cromwell, second son of Sir Oliver Cromwell, and first cousin to the renowned Oliver Cromwell. She and John had a son and a daughter. The fire of 1673 which destroyed the Navy Office started in her private closet: this is unlikely to have improved her relations with Samuel Pepys, whose private apartments were destroyed in the blaze.