Which cardinal urged Copernicus in 1536 to publish his heliocentric theory?

The cardinal who urged Copernicus in 1536 to publish his heliocentric theory was Nikolaus von Schönberg.

On 1 November 1536, Schönberg wrote to Copernicus from Rome after hearing about his revolutionary claim that Earth moves and that the Sun occupies the central position. Schönberg praised Copernicus's astronomical skill and asked him to send his writings, tables, and explanation of the celestial system to scholars.

Schönberg went further than simply offering encouragement: he arranged for Copernicus's work to be copied and offered to pay the expenses. Copernicus eventually published De revolutionibus orbium coelestium in 1543, seven years after the letter. He included Schönberg's letter in the book's introductory material, helping preserve the cardinal's role in the story of heliocentrism.

A common mix-up is to identify Galileo's later defenders or critics, such as Robert Bellarmine, with this earlier appeal. Schönberg was a German cardinal and former Archbishop of Capua, and he died in 1537, before De revolutionibus appeared.