St Seraphim (1754-1833) is remembered for his humility and faithfulness in the face of suffering, as well as his gentleness with those he came into contact with, even those who did him wrong.
He lived as a monk and then a hermit for much of his life. He recieved remarkable healings and visions of both the Theotokos (mother of God) and Jesus himself. His teachings were centred in prayerfullness and the seeking of the Holy Spirit.
His most remembered sayings are:
"Acquire a peaceful spirit, and around you thousands will be saved.“
"It is necessary that the Holy Spirit enter our heart. Everything good that we do, that we do for Christ, is given to us by the Holy Spirit, but prayer most of all, which is always available to us."
Here is the Wikipedia page with information about St Seraphim.
Here is a video about his life and legacy.
Here is a 7 minute sermon from the Holy Ghost Orthodox Church in Bridgeport where Fr John Jillons recounts his story.