The sketch on the left is Yuji Horii, the main designer behind Dragon Quest, sending Toriyama a basic fantasy slime inspired by the western PC RPGs that he and his programmers were all into. Toriyama went "no, lets make it a funny little guy" and designed the iconic design on the right. With its memorable shape and face. And it became a series mascot that endures in Japan as one of the most iconic series mascots and printed Enix, and now Squarenix, a bajillion dollars.
https://thomaswell.medium.com/the-story-behind-dragon-quest-c914a7bd3d74 https://www.polygon.com/gaming/24094509/akira-toriyama-dragon-quest-slime https://xcancel.com/hamishsteele/status/1623436759215534080
Goku started as a funny lil guy. He just grew into a big funny lil guy