Saint Seraphim of Sarov (Russian: Серафим Саровский) (30 July [O.S. 19 July] 1754 (or 1759) – 14 January [O.S. 2 January] 1833), born Prokhor Moshnin (Прохор Мошнин), is one of the most renowned Russian monks and mystics in the Orthodox Church. He is generally considered the greatest of the 19th century startsy (elders) and, arguably, the first. He is remembered for extending the monastic teachings of contemplation, theoria and self-denial to the layperson, and taught that the purpose of the Christian life was to acquire the Holy Spirit.
Seraphim was glorified (canonized) by the Russian Orthodox Church in 1903. The date of his death is his major feast day. Reverence for him is not limited to the Orthodox; Pope John Paul II referred to him as a saint in his book, Crossing the Threshold of Hope.[1][2]
One of his "spiritual children", Nicholas Motovilov, wrote most of what we know about him today.
Perhaps Seraphim's most popular quotation amongst Orthodox believers is "Acquire a peaceful spirit, and thousands around you will be saved."
en.wikipedia.org/wiki/Seraphim_of_Sarov