The use of onomatopoeia in comics dates back to the early twentieth century.  Roy Crane, the creator of Captain Easy and Buz Sawyer, seems to have an great impact on the popularisation of onomatopoeias:
"It was Crane who pioneered the use of onomatopoeic sound effects in comics, adding "bam," "pow" and "wham" to what had previously been an almost entirely visual vocabulary. Crane had fun with this, tossing in an occasional "ker-splash" or "lickety wop" along with what would become the more standard effects. Words as well as images became vehicles for carrying along his increasingly fast-paced storylines."
(Tim DeForest, 2004:116)