Zyobot
Just a time-traveling robot stranded on Earth.
FWIW, I was thinking of someone who was not particularly well-known in real life--someone who will gradually emerge out of the shadows after Stalin's death and cultivate people with his charisma. It could even be an ordinary person just so long as he won't get liquidated before he's able to seize power.
Well, we've had plenty of mountain-moving dark horses who'd have otherwise died unknown and insignificant IOTL, so I suppose there's room for that, too.
Problem is, that doesn't leave us with much to work with, unless we either extrapolate what their counterparts may be like to the extreme or come up with entirely fictional characters to fill the void.