| Mikalojus "the Old" Radvila | |
| Death Date: | 16 July |
| Noble Family: | Radziwiłł |
| Spouse: | Sofija Ona Manvydaitė Zofia Zasławska Fiedora Rohatyńska |
| Issue: | with Sofija Ona Manvydaitė: Mikolaj Radziwiłł Jan Radziwiłł Anna Radziwiłł Wojciech Radziwiłł Jerzy Radziwiłł |
| Father: | Radvila Astikas[1] |
| Mother: | Eudoxia Radziwiłł |
Mikalojus Radvila or Mikołaj I[2] nicknamed the Old (Lithuanian: Mikalojus Radvilaitis, Mikalojus II Radvila Senasis, Polish: Mikołaj Radziwiłłowicz Stary, Latin: Nicolaus II Radziwil Priscus) ( - 16 July 1509) was a Lithuanian noble. He was known after a patronym Radvilaitis, made of his father's name Radvila, which in turn became a family name of his heirs, Radvilos, which later polonised as Radziwiłł.
Mikalojus had been a regent of Smolensk from 2 December 1481; in 1483 a 10,000-strong army was summoned by him for protection of Smolensk lands. He had been the Castellan of Trakai since 31 May 1488 and regent of Novgorodok, later a regent of Bielsk Podlaski. He was the Voivod of Vilnius since 1492 and the first Grand Chancellor of Lithuania from 1504 until his death in 1509. His sons Jerzy, Mikołaj, and Jan were the progenitors of the three Radziwiłł family lines. His daughter Anna was the great-grandmother of Elizabeth Báthory.