Ivor Bertie Guest, 1st Baron Wimborne, 2nd Baronet Dowlais DL (29 August 1835 – 22 February 1914) was a Welsh industrialist.
Sir Ivor Bertie Guest was born at Dowlais, near Merthyr Tydfil, the son of Lady Charlotte Guest, translator of the Mabinogion, and Sir John Josiah Guest, 1st Baronet Dowlais, owner of the world's largest iron foundry, Dowlais Ironworks. His middle name (Bertie) was from his mother's family, the Earls of Abingdon, descended from a Tudor courtier who married the Dowager Duchess of Suffolk, and herself suo jure Baroness Willoughby de Eresby. His siblings included: Montague Guest (1839–1909), a Liberal politician, Arthur Edward Guest (1841–1898), a Conservative politician, Charlotte Maria Guest (d. 1902), Mary Enid Evelyn Guest, who married Austen Henry Layard, and Blanche Guest, who married Edward Ponsonby, 8th Earl of Bessborough.
Guest was educated at Harrow School in Middlesex, and went on to gain a Master of Arts degree from Trinity College, Cambridge in 1856.
Guest succeeded his father to his baronetcy following his death in 1852. He was elevated to the peerage in 1880 as Baron Wimborne, of Canford Magna in the County of Dorset, on Disraeli's initiative.
He was commissioned a cornet in the Dorsetshire Yeomanry on 20 April 1858 and was promoted lieutenant on 11 March 1867.
He held the office of High Sheriff of Glamorgan in 1862 and was the mayor of Poole from 1896 to 1897. In 1879 he rebuilt the real tennis court at Canford. He was lampooned in Vanity Fair as "the paying Guest".
From 1874 on, he stood unsuccessfully for election to the House of Commons as a Conservative, contesting Glamorganshire at the 1874 general election, Poole at a by-election May 1874, and Bristol at a by-election in 1878 and at the 1880 general election. However, following the tariff reform by Chamberlain he seceded from the Conservative party and sat in the House of Lords as a Liberal.
He was President of the Dean Close Memorial School from 1902. and a Deputy Lieutenant of Dorset.
On 25 May 1868, Guest married Lady Cornelia Henrietta Maria Spencer-Churchill (1847–1927). She was the daughter of John Spencer-Churchill, 7th Duke of Marlborough, thus making Guest an uncle-by-marriage of Sir Winston Churchill, later the Prime Minister of the United Kingdom. Together, they had:
- Frances Guest (1869–1957), later known as Lady Chelmsford, who married Frederic Thesiger, 1st Viscount Chelmsford, who served as Viceroy of India.
- Ivor Churchill Guest (1873–1939), who married Hon. Alice Grosvenor (1880–1948)
- Christian Henry Charles Guest (1874–1957), who married Hon. Frances Lyttelton (1885–1918)
- Frederick "Freddie" Edward Guest (1875–1937), a Liberal politician
- Oscar Montague Guest (1888–1958), who married Kathleen Paterson (b. 1903)
He died on 22 February 1914 at Canford Manor in Dorset and was succeeded by his son, Ivor Churchill Guest, 2nd Baron Wimborne, 1st Baron Ashby St Ledgers, who was later created Viscount Wimborne. His will was probated in April 1914, provisionally at £250,000.
In 1867, Guest bought at auction "Hamilton House" located at 22 Arlington Street in the St. James's district of the City of Westminster in central London from the widow of William Hamilton, 11th Duke of Hamilton. As the house had traditionally been renamed with the title of each peer who owned it, upon receiving his title in 1880, Guest renamed the house "Wimborne House".