St. Sergius' successor as monastery abbot was St. Nikon (1355-1426), 1st among his disciples, from 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 coworker. Half a year before his death, St. Sergius entrusted the monastery leadership to St. Nikon and vowed himself to silence. He was monastery abbot until his death.
St. Nikon rebuilt the entire monastery destroyed during the invasion by Han Edigey 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 Andrey Rublev and Daniel the Black to paint the cathedral. The work was finished by 1425.
St. Nikon 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 its western wall there is a chapel called Serapion’s Tent, constructed above the tomb of St. Serapion, a Novgorod archbishop.