Vicious gatekeeper who found employment in Barking? (8)

I believe the answer is:

cerberus

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'vicious gatekeeper' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I don't see?

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

Can you help me to learn more?

(Other definitions for cerberus that I've seen before include "Mythical three-headed dog that guarded Hades" , "Three headed guard dog of Hades" , "underworld guard" , "Mythical three-headed watchdog guarding Hades" , "Hades gate guardian" .)

I've seen this clue in The Telegraph.

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