Temper originally consuming Caligula? (7)

I believe the answer is:

emperor

I'm a little stuck... Click here to teach me more about this clue!

'consuming caligula?' is the definition.
The definition suggests a singular noun which matches the answer.

'temper originally' is the wordplay.
'EMPEROR' is hidden within the letters.
However, I'm unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for emperor that I've seen before include "Beethoven piano concerto, Op. 73" , "He rules over several states" , "Ruler of large territory" , "Male ruler of a group of countries" , "A moth; a penguin" .)

I've seen this clue in The Telegraph.

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