St. Nikon (1355-1426) was from the city of Yuriev-Polsky (half way between Rostov and Radonezh). He came to the Trinity monastery at a very early age, that’s why St. Sergius put him under the guidance of his disciple St. Athanasius, the abbot of the Theotokos on the Mountain monastery in Serpukhov. In 1375 St. Nikon returned to the Trinity monastery and became St. Sergius` closest co-worker. Half a year before his death, St. Sergius entrusted the leadership of the monastery to St. Nikon and vowed himself to silence. He was abbot of the monastery until his death in 1426.
St. Nikon rebuilt the entire monastery that had been destroyed during the invasion by Khan Edigei in 1408. In 1422 the holy relics of St. Sergius were discovered during the construction of the Trinity Cathedral. St. Nikon commissioned the famous iconographers Andrei Rublev and Daniel the Black to paint the cathedral. The work was finished by 1425.
St. Nikon died in 1426 and was buried by the southern wall of the Trinity Cathedral, where a church dedicated to him was constructed in 1548, a year after his canonization. The church was rebuilt in 1623. At the western wall of it there is a chapel called Serapion’s Tent, constructed above the tomb of St. Serapion, archbishop of Novgorod.