It is historically accurate to identify the extreme left with the ComIntern, i.e. the Soviet communist party, ruled during his lifetime by Stalin. Almost all communist parties were in the mould designed by Lenin, and refined by Stalin.
Even today, socialist / communist parties operate using the Leninist style of organisation, e.g. in the UK the SWP or RS21.
It is useful to know this, just as it's useful to know that Cambridge Analytica was owned by a company whose board is full of UK military/security-service types [1].
[1] http://bellacaledonia.org.uk/2018/03/20/scl-a-very-british-c...