A Russian tankie is someone that intensively promotes the Soviet Union and its ideology.
A tankie is someone who takes Marxism as serious as their own religion, they live for it. They believe Marx’s theories are perfect, they read everything that was written by Marx himself and believed that with Russia making everything equal, world peace would be achieved. And in a way, they were right to think so at least for a while the Soviet Union had strict orders under Stalin to make sure everyone gets what they need, but when he died it stopped coming out of desperation for power other people wanted him dead so bad there was nothing going on his fear was too much a few years back before he died he began attacking instead of giving up and Russia was quickly on the edge of death and it never fully recovered and never became what people thought it would be.