Short answers, pulled from the story.
Michael Andreas Barclay de Tolly was a Russian field marshal of Baltic German descent who played a central role in defeating Napoleon's invasion of Russia in 1812. Born on the 27th of December 1761 (baptism date), he rose from enlisting in the Pskov Carabineer Regiment in 1776 to commanding the largest Russian army facing Napoleon and eventually leading the taking of Paris in 1814.
Barclay de Tolly ordered a scorched earth retreat from the start of the campaign, burning supplies and land to deny the French army any means of sustaining itself deep in Russian territory. The strategy made him deeply unpopular at the time, and he was accused of cowardice and even of being Napoleon's agent, but it was ultimately credited with exhausting and destroying the Grand Army.
Public and military outcry over the loss of Smolensk forced Tsar Alexander I to appoint Mikhail Kutuzov as overall commander-in-chief in August 1812. Barclay's non-Russian origins fed suspicion of his loyalties, and his subordinates and the Tsar pressured him to engage the French before he believed conditions were right. He remained in command of the 1st Army of the West under Kutuzov.
In 1809, during the Finnish War against Sweden, Barclay led approximately 3,500 troops approximately 100 kilometers across the frozen Gulf of Bothnia in winter through a snowstorm, then seized Umeå in Sweden. The exploit was immortalized by the Russian poet Baratynsky and earned Barclay promotion to General of the Infantry and appointment as Governor-General of Finland.
The Barclay de Tolly family were German-speaking descendants of the Scottish Clan Barclay. Their ancestor Peter Barclay, of the Towie or Tolly branch, settled in Rostock in 1621, and his son later moved to Riga in Livonia. Michael Andreas was raised in the Baltic world and in St. Petersburg, making him culturally distant from the Russian officers who later questioned his loyalties.
Barclay received the 1st class Order of St. George on the 19th of August 1813 for the defeat of the French at the Battle of Kulm. His effective command of Allied central forces at Leipzig in October 1813 earned him the title of count from the Tsar. For commanding the taking of Paris in 1814, he was awarded the baton of a Field Marshal, and at the close of the 1815 campaign he was elevated to the rank of prince.