Question

who was the first to assume the title of Tsar?​

Answer 1

Ivan IV

The title was used by only two monarchs between 1345 and 1371, as previously early royalty had used the Serbian royal title for king. The first Russian ruler to be formally crowned “tsar of all Russia” was Ivan IV, known until then as “grand prince of all Russia” in 1547

Answer 2

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However, the title "tsar" (and its Byzantine Greek equivalent basileus) was actually adopted and used for the first time by his son Simeon I, following a makeshift imperial coronation performed by the Patriarch of Constantinople in 913.