Tintinologist.org: Adventure of Shouchan - great rival of Tintin
"SHOUCHAN is a very old MANGA character created in the early part of the 20th century in Japan. His first story, OTOGI SHOCHAN NO BOUKEN was created in 1923! SHOUCHAN is a youth journalist for the newspaper, ASAHI. He has a talking animal friend - a large chipmunk, called RISU. The adventures of Tintin are very realistic, but adventures of Shouchan are more fantasic. He goes to heaven, encounters monsters and Kentauros".
Other web references also seem to suggest that Shochan appeared in 1923 while Tintin first appeared in 1929.
