Alexander Barclay de Tolly-Weymarn
|Birth name||Alexander Magnus Friedrich von Weymarn|
|Born||December 22, 1824|
Pärnu, Governorate of Livonia, Russian Empire
|Died||May 8, 1905|
Dresden, Kingdom of Saxony, German Empire
|Service/||Imperial Russian Army|
|Commands held||Pavlovsky Regiment|
24th Infantry Division
1st Army Corps
|Battles/wars||Russo-Turkish War (1877-1878)|
Prince Alexander Magnus Friedrich Barclay de Tolly-Weymarn (Russian: ?---?, Alexander Petrovich Barklay-de-Tolli-Veymarn; December 22, 1824 - May 8, 1905), born as Alexander Magnus Friedrich von Weymarn, was a Baltic German military commander who served in the Imperial Russian Army.
He was a member of the Baltic German nobility, and the son of General Wilhelm Peter Jost von Weymarn (1793-1846) and his wife, Christina Augusta von Lueder (1803-1887). He married Marie Friederike von Seddeler in 1849 and had three children: daughters Alexandrine "Ada" Auguste Olga Barclay de Tolly-Weymarn and Marie "Mira" Georgia Augusta Barclay de Tolly-Weymarn, and son Ludwig Alexander Michael Barclay de Tolly-Weymarn.
His maternal grandmother was the sister of Prince Michael Andreas Barclay de Tolly, a very prominent military commander who was made a count in 1813 and a prince in 1815 by Alexander I of Russia. After the extinction of the original Barclay de Tolly princely line upon the death in 1871 of Prince Michael's son (Magnus Barclay de Tolly), Alexander von Weymarn was allowed to assume the title of Prince Barclay de Tolly-Weymarn in 1872, by permission of Alexander II of Russia.