If you had paid close attention you may have seen this character often on Astroboy or the Amazing 3. It is in Astroboy #1, and also the Monster Machine, and check the A3 "Autopictagraph" episode and you will see him as a gas-bomb. So, what is it you may ask??
This "funny face" is hyoutan-tugi (sewed gourd). Tezuka always used that character to "cool down" the scene when its getting too serious. He said "I'm too shy (embarrassed) to keep the story serious, so this nonsense character was useful to cool down the story, and also useful to hide how shy I am." It is said when he was a kid, he created that character from his little sister's drawing. He stopped using it in the 80s. From the late 70s, his manga became non-fantasy. He made many realistic mangas.
BTW, Tezuka himself is shown in some of his Anime-series as a certain character. In his manga, he sometimes appears in his work. Sometimes, as one of a group of characters, and sometimes as Tezuka himself...(and sometimes he's also been killed in the story!)
Also "Hige-Oyaji", the bald-headed guy with a white mustache, you Astro fans would know him as: Mr. Pompous...this character was designed when Tezuka was just a child. He said its design came from a Donald Duck cartoon.
I heard that Proffessor Ochanomizu's nose was designed by a mistake. While drawing him Tezuka's pen slipped and drew a great big nose on his face, and Tezuka said, "This is it"!
Tezuka also said that Astro-boy is a girl! Well, Astro Boy is looks like a boy, but for Tezuka he was kind of a "uni-sexual" character. So he said honestly he didn't want to make Astro Boy's brothers. (As you know, Astro Boy has a young brother and a sister - Astrogirl)
Well, no I didnt know Astro had a younger brother, maybe well find out more about him later!