Short answers, pulled from the story.
Pavel Mikhailovich Tretyakov purchased two paintings by Russian artists in 1856. This transaction marked the founding year of what would become the State Tretyakov Gallery.
The official opening of the museum called the Moscow City Gallery of Pavel and Sergei Tretyakov took place on the 15th of August 1893. The gallery was located in a mansion that the Tretyakov family had purchased in 1851.
Architect V. Bashkirov designed the famous façade based on drawings by the artist Viktor Vasnetsov. The style was a peculiar Russian fairy-tale aesthetic constructed to the south from the Moscow Kremlin.
On the 3rd of June 1918, the Tretyakov Gallery was declared owned by the Russian Federated Soviet Republic. It received the name State Tretyakov Gallery at that time.
During the decade when the main gallery closed for major renovation, the only museum open to visitors was the building on Crimean Val, number ten. This branch had been merged with the Tretyakov Gallery in 1985.