Earliest Rastafarians backed Russian boss (4)

I believe the answer is:

tsar

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'boss' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for tsar that I've seen before include "Powerful man" , "Ruler finally executed" , "Rats (anag)" , "Formal rulings on Islamic law; was aft (anag.)" , "Supreme authority" .)

I've seen this clue in The Daily Mail.

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