When Mitchell mentioned that Ivan was 237 years old on a recent episode of 'Being There', the Russian vampire said nothing to dispute the claim. So that means Ivan was "embraced into the Kindred" around 1773. And there were two major events in Russia around that time when vampires had plenty of opportunities to feed and create new vampires:
Emelian Pugachev started a rebellion in Russia.
The Russo-Turkish War, 1768-1774: Russian forces failed to take Silistria in 1773.
Under the chaotic cover of such carnage, Ivan may have been a mortally wounded Russian soldier who was turned by some vampire who took a fancy to him....