Brett and Chet are the Once-ler's older brothers, they are slightly on the dumb side and violent for their age, which is rumored to be 25. They are, in other words, mamma's boys and they'll do everything she says, only to fear that she'll yell at them, and while it doesn't seem like it, they do secretly love their younger brother. Playfully abusing him and teasing him when he does something that they find frivolous or dumb is just their way of love. However, they may become rather violent and destructive when carrying out their mother's orders. They may want to hurt Once-ler when he steps out of line
They aren't very talkative, and in the beginning of Once-ler's rise to sucess, their only job is to try to pick the tufts off of the Truffula trees, but that soon gets too hard and they are moved on to work with the axe-hanking machine, which chops down the trees instead. Once Once-ler is at the top of his business and has his factory, Brett and Chet started working as his guards and doormen.
When Once-ler fails and loses his whole company, due to having no more material for his Thneed, Brett and Chet pack up with the rest of the family and go back into their van, soon shocked when their mother informs them that Brett is now her favorite son, pretty much disowning the Once-ler as they then drive off.