Although the origin of Plastic Man was never related on the show, his name is Patrick "Eel" O'Brian, and he was a thief who broke into a plastic factory with a few of his friends for a heist and was doused in experimental plastic.
Plastic Man is actually a rubber man. He got his name because there was already a hero owned by MLJ (now Archie Comics) called 'Flexo the Rubber Man' at the time that Plastic Man made his debut in the 1940s.
In the cartoon, Penny and Hula-Hula were Plastic Man's sidekicks. In the comics, however, his sidekick was Woozy Winks.
Season One episodes (under the title "The Plastic Man Comedy/Adventure Show") ran for two hours and included two "Plastic Man" cartoons, two "Mighty Man and Yukk" cartoons, a "Rickety Rocket" cartoon, and a "Fangface and Fangpuss" cartoon. In January 1980, the series was cut down to 90 minutes and dropped a "Rickety Rocket" cartoon entirely. Season Two episodes (rebranded as "The Plastic Man - Baby Plas Super Comedy Show" or "The Plastic
Man - Heathcliff - Thundarr Show") ran in its same 90 minute time and featured "Plastic Man", "The Plastic Family", and "Baby Plas" cartoons, a Heathcliff (1980) cartoon and a Thundarr the Barbarian (1980) cartoon.
A Plastic Man animated series was in early development at Filmation in 1967 around the time the third season of New Adventures of Superman, second season of Aquaman, and a new series in Metamorpho were being animated. However, the cancellation of Batman saw Filmation swoop in to pick up its license to produce a cartoon for the character. Thus, all superhero projects save Superman were cut so that the Batman cartoon could make it to air by the next fall season.