Why was Joseph Stalin reffered to as the grey blur?

Stalin became known as the 'Grey Blur' because of his tactics.

On his way into power he tried to be as sneaky as possible, playing his political opponents off against each other, and tricking them into making poor decisions until he no longer had any opposition. He was able to do this because he had no concrete set of values of beliefs, so he could effectively change his opinion to anything in order to obtain power.