Crossword Genius

In 'Batman', the cardboard character? (5)

Ross

I believe the answer is:

joker

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'character?' is the definition.
(thesaurus)

I don't understand the rest of the clue.

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(Other definitions for joker that I've seen before include "Comic; a card" , "Humorist" , "trickster" , "Playing card" , "Jester" .)

I've seen this clue in the Evening Standard.
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