Alexander (Russian Александр) was born on May 13, 1221 at Pereslavl-Zalessky to Grand Prince Yaroslav II of Vladimir — the grandson of Grand Prince Vsevolod III the Big Nest and the great-great-grandson of Vladimir Monomakh.
At the age of 15 in 1236, Alexander was appointed Prince of Novgorod — the principal northwestern Russian city-state and the frontier of the Russian Catholic-Orthodox territory against the Catholic Latin Crusader and pagan Baltic states.
On July 15, 1240 — at the age of 19 — Alexander won the famous Battle of the Neva against the Swedish Catholic Crusader army led by Birger Magnusson at the confluence of the Izhora and Neva rivers. The victory earned Alexander the famous surname Nevsky ('of the Neva') and saved the Russian northwestern territory from the Swedish Catholic Crusader advance.
On April 5, 1242, Alexander won the even more famous Battle of the Ice (Ledovoye Poboishche) on the frozen Lake Peipus (Chudskoye Lake, on the border of Russia and Estonia) against the Teutonic Knights (the German Catholic Crusader military-religious order that had been advancing into the Baltic and northwestern Russian territories). The Russian victory decisively ended the Teutonic Knights' advance into the northwestern Russian territory — institutionally securing the eastern-Catholic-Orthodox Russian national identity against the Latin-Catholic Crusader advance.
The Battle of the Ice is the most famous single military engagement of the medieval Russian Catholic-Orthodox tradition — the subject of Sergei Eisenstein's famous 1938 Soviet film 'Alexander Nevsky' (with the famous Prokofiev-composed cantata 'Alexander Nevsky', one of the principal 20th-century orchestral works).
In the aftermath of the Mongol invasions of 1237–1240 (which had destroyed most of the southern Russian territory), Alexander adopted the diplomatic-political strategy of submission to the Golden Horde (the Mongol Khanate of Sarai) and simultaneously military resistance to the Latin-Catholic Crusader west — the 'submit to the East, resist the West' policy that would shape the Russian political-cultural orientation for the seven centuries.
In 1252 Alexander was elevated by the Golden Horde Khan Batu to be Grand Prince of Vladimir — the principal Russian royal title of the period. His eleven-year Grand-Princely reign (1252–1263) was devoted to the rebuilding of the Russian ecclesiastical and civil institutions under Mongol overlordship and to the continuing military resistance to the western Catholic advance.
Returning from a diplomatic mission to the Mongol court of Sarai in autumn 1263, Alexander fell ill at Gorodets on the Volga; on the eve of his death, he took the monastic habit under the monastic name Aleksy — the classic Russian royal-monastic transition. He died on November 14, 1263.
His canonization by the Council of Moscow in 1547 under Metropolitan Macarius institutionally established Alexander as one of the principal Russian Catholic-Orthodox national saints. His relics were translated on August 30, 1724 by Emperor Peter the Great from the Nativity Cathedral in Vladimir to the new Alexander Nevsky Lavra in Saint Petersburg — the new Russian imperial capital, institutionally re-orienting the Russian national identity to the new Petrine imperial-modern political-cultural project.