Your answer would be the following one: One hero in the animation field is Mel Blanc the voice behind many cartoon characters.
Explanation:
An appositive is a noun or noun phrase that renames another noun right beside it. In the sentence above, the appositive "the voice behind many cartoon characters" renames the noun "Mel Blanc". However, the sentence is wrongly punctuated because there should be a comma before the appositive phrase.
Nonessential appositive phrases are always separated from the rest of the sentence with commas to indicate that if they were removed, the meaning of the sentece would be left unchanged. In the sentence above, "the voice behind many cartoon characters" is not essential information to the reader because Mel Blanc being important in the animation field can be inferred from previous information (one hero in the animation field). That is the reason why there should be a comma before the appositive phrase.
