Semyon Ivanovich Yanovsky, known in monasticism as Schema-Monk Sergius, was born on April 15 (26), 1789, in Glukhov, Chernigov province. He was a captain of the 2nd rank and served as the chief ruler of Russian America in 1818 and 1820. Yanovsky left behind a diary in which he described his voyage from Sitka Island to Okhotsk and his journey from America to St. Petersburg.

Yanovsky was born into the family of a retired army captain who served as an official in the district court. In 1808, he graduated from the Naval Cadet Corps and served in the Baltic Sea until 1816, attaining the rank of lieutenant in 1812. From 1816, Yanovsky served in the Russian-American Company and participated in a circumnavigation on the ship 'Suvorov' under the command of L. A. Gagemeister. In the summer of 1817, he arrived in Russian America and was appointed chief ruler of Russian America in October 1818. During an inspection trip to Kodiak Island, Yanovsky became close to the monk Herman, who had a significant spiritual influence on him, and Yanovsky became a deeply believing Christian.

On September 11, 1820, Yanovsky transferred his duties to the new ruler Matvey Ivanovich Muravyov and set off to St. Petersburg via Okhotsk and Siberia. In the capital, he was assigned to the 15th Naval Crew and in 1824 received the rank of captain-lieutenant, and in 1826, captain of the 2nd rank, after which he retired.

In 1834 and 1852, Yanovsky served as the director of the Kaluga provincial gymnasium, after which he moved to his estate. At the end of 1865, he settled in Tikhonova Pustyn, where in 1866 he took monastic vows under the name Sergius and in 1873 was tonsured into schema. He spent his last years in the Sretensky Skete.

His letters to the abbot of the Valaam Monastery, Damaskin, became the basis for the lives of St. Herman of Alaska and the martyr Peter the Aleut.

From his first marriage to the daughter of the ruler of Russian America, Alexander Andreyevich Baranov, Yanovsky had two children. In 1826, he remarried after the death of his first wife Irina in 1824. From his second marriage, he had children: Nikolai, who became the Kaluga provincial leader of the nobility and a member of the State Council, and Ivan, a cadet of the Naval Cadet Corps, who died from wounds during the defense of Sevastopol.

A mountain on Sitka Island is named in honor of Yanovsky.