[Contextual image: music notes, two +1 markings]
Name that actor
_ _ _ _ _ _ C _ _ _ _
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The missing actor is
Let's take the notes on the staff,
convert them to numbers (A=1, etc.), and sum them together when connected by a bar:
"Huge Yakman" which might be mistaken for our answer which fits the provided blanks: Hugh Jackman!
As for the title,
"Grunniens" is the scientific name for a yak.
OP Addition - In 2021 Hugh Jackman played Harold Hill in The Music Man.