Dad and I voiced early cartoon character (6)
I believe the answer is:
popeye
'early cartoon character' is the definition.
(Popeye is a comic strip character)
'dad and i voiced' is the wordplay.
'dad' becomes 'pop' (synonyms).
'and' says to put letters next to each other.
'voiced' shows a homophone (sound like).
'i' is a homophone of 'eye'.
'pop'+'eye'='POPEYE'
(Other definitions for popeye that I've seen before include "Cartoon spinach eater" , "I eat spinach" , "Spinach and Olive Oyl lover" , "Cartoon sailor (showing amazement?)" , "Old cartoon sailor" .)