Once Ler is the main protagonist in The Lorax, both the movie and the novel.
The Once-Ler's childhood was all kinds of screwed up!
Born and raised on a farm, his family had to make a living off of, well, farming! With their father gone, Once had to lead his household as the 'man of the house'. He was the eldest Ler, and he was the smartest one under that roof! He was raised under a One-Tear Policy. He couldn't spend any time crying. Not with a family's stabilization on his shoulders.
He had to work under child labor to keep his family up without Therd Ler. That's... how he sprained his wrist pretty badly at 11.
Once and Airabella were, unfortunately, prone to sickness as children. The twins weren't as vulnerable, but there was one time where all four of them were sick for at least two weeks with terrible conditions. Because they were poor as well, they were all fairly close to death, which is how Once's little sister died.
School was Once-Ler's safe-zone. He didn't have to endure his mother's manipulation, and he could feel free to be himself. He graduated high school with honors, boney body and all. He wanted to attend college, but he wouldn't be able to until he left for the Truffula Forest.
His only friend was Norma Pacey, and it wasn't until he met her that he came up with the idea for the thneed! He figured that he could create something that gave everyone whatever it was THat they NEEDed.
When he and his brothers were grown up, their property was being threatened. So, in attempt to compromise, Once went with his mother to make a deal with a banker. Unfortunately, the banker's morals were in the dirt, so he wasn't willing to help unless Once gave him something that the Ler thought should never be tossed up.