Although most truck drivers work for a larger trucking company, this is not the only way to make a living as a driver. Owner-operators own their own trucks and trailers instead of using company-owned equipment, and can work on their own or rent the machines to another company. This independence comes at a higher cost, but you can still get much more for it.
Most of the homeowner operators had been in the trucking business for several years, either as dispatchers or drivers, before becoming independent. Owning your own truck/trailer means paying maintenance costs out of pocket, which may not be a very attractive prospect for some drivers.
If you can handle the upfront costs and are willing to take responsibility not only for yourself but also for other employees, becoming an owner operator might be a great idea.