Prince Mikołaj Krzysztof Radziwiłł[n 1] (Lithuanian: Mikalojus Kristupas Radvila; 2 August 1549 – 28 February 1616), nicknamed "the Orphan" (Polish: Sierotka, Lithuanian: Našlaitėlis), was a Polish–Lithuanian nobleman (szlachcic), Ordynat of Nyasvizh from 1586, Court Marshal of Lithuania from 1569, Grand Marshal of Lithuania from 1579, castellan of Trakai from 1586, voivode of Trakai Voivodeship from 1590, voivode of Vilnius Voivodeship from 1604 and governor of Šiauliai.

[1] However, he also refused to support the Krzysztof 'Piorun' Radziwiłł, whose conflict with another powerful family threatened to plunge the Grand Duchy into a civil war.

Robert Burton while on the subject of St. Elmo's fire wrote of this voyage in his Anatomy of Melancholy: "Radzivilius, the Polonian duke, calls this apparition, Sancti Germani sidus; and saith moreover that he saw the same after in a storm, as he was sailing, 1582, from Alexandria to Rhodes".

[citation needed] While in Rome, he met Piotr Skarga and Stanislaus Hosius, who convinced him to convert from Calvinism to Catholicism, as later did his other brothers, many upon his insistence.

[1] One of the chapels in the Jesuit church in Nesvizh, founded by Mikołaj Krzysztof, would become the family's mausoleum for the Radziwiłłs, serving them for the next two hundred and a half centuries.