Alexander Forbes Irvine, 20th Laird of Drum FRSE JP DL LLD (1818-1892) was a Scottish landowner, advocate, philosopher and amateur astronomer. He was a prominent member of Clan Irvine and held the family seat of Drum Castle until his death.
He was born at Schivas House near the village of Tarves in Aberdeenshire on 18 February 1818, the son of Alexander Forbes Irvine, 19th Laird of Drum (1777-1861), and his wife Margaret Hamilton of the Hamiltons of Little Earnick. He was a friend of his near neighbour, Cosmo Innes, and their careers followed very parallel paths. Other friends included William Forbes Skene of Rubbislaw and Sir David Lindsay.
He was home tutored rather than attending school, then studied Law first at Marischal College in Aberdeen University then at Edinburgh University. He passed the Scottish bar as an advocate in 1848 and rose to be Dean of the Faculty of Advocates. He was Principal Clerk of the Justiciary Court 1867 to 1874 and Sheriff of Aberdeenshire from 1874 onwards.
He inherited the Drum Estate in 1861, on the death of his father.
In 1878 he was elected a Fellow of the Royal Society of Edinburgh. His proposers were Sir Alexander Grant, Charles Neaves, Lord Neaves, Edward Sang and Peter Guthrie Tait. He twice served as Vice President to the Society: 1883 to 1887 and 1890 to 1892.
In 1886 he co-founded the New Spalding Club. In 1887 Edinburgh University awarded him an honorary doctorate (LLD).
He died at Drum Castle on 4 April 1892.
In 1848 he was married to Anna Margaretta Forbes-Leslie (d.1900), daughter of Lt Col Jonathan Leslie of Rothienorman, a noted amateur archaeologist.