Adolf "Ulf" Konstantin Jakob Freiherr Pilar von Pilchau (23 May 1851 – 17 June 1925) was a Baltic German politician and regent of the United Baltic Duchy (1918).
Adolf Konstantin Pilar von Pilchau was born on the 23 of May 1851. He came from the German-Baltic noble family Pilar von Pilchau, who were in the service of the Swedish and Russian crowns. His parents were Fredrik Adolf Woldemar Baron Pilar of Pilchau, Lord of Audern (1814–1870) and Berta Johann Caroline von Ungern-Sternberg from the House of Grossenhof (1826–1903).
Pilar von Pilchau became the owner of the Audern manor, his birthplace after his father's death in 1870. In 1881 he rented Sauck manor. Both are situated in modern Pärnu County, Estonia.
He started his political and administrative career in 1876 as a judge in the first district of Pernau (Pärnu) and proceeded from there to the position of Pernau city councillor in 1879. Three years later he began working for the Livonian Noble Corporation, the local government. He filled in the position of the treasurer. In 1899 he was elected the land councillor of Livonia which was a high position in the local government of Baltic Germans.
From 1908 to 1918 von Pilchau served as the of Livonia, the leader of the noble corporation. From 1912 to 1917 he was also a member of the State Council of Imperial Russia as a representative of Livonia.
He was one of the persons behind the creation of the short-lived United Baltic Duchy and the only Chairman of its Regency Council from the 5 to the 28 November 1918.
On 3 January 1919, Pilar von Pilchau went into exile and lived for several years in Weimar Germany. He returned to an independent Estonia in 1923 with his wife and settled in Pärnu where he died on the 17th of June 1925.