Lazar the Hilandarian or the Serb (Serbian: Лазар Хиландарац, Србин Лазар/Лазар Српски; fl. 1404) was a Serbian Orthodox monk in the Hilandar monastery (hence his epithet) of Mount Athos, and an architect, the first known Serbian and Russian watchmaker.
Lazar was born in Prizren, in the Serbian Empire. He designed and built the clock and clock tower itself that stood in the Grand Prince’s palace behind the Annunciation Church in 1404. This was made on the request of Vasily I of Moscow. The clock functioned for 217 years.