In the mid 1800's as businesses grew they acquired more employees who did solely clerical work. These workers needed office chairs in order to be able to sit and work for extended periods of time without pain or discomfort.
The office chair was designed with productivity in mind. The typical office chair has a swiveling seat to allow the reach of many documents without having to stand up; as well office chairs have a backrest to prevent discomfort while sitting for long periods of time. Most office chairs also have arm rests to provide support while the workers uses a computer or other device.
Currently there are many styles of office chairs to choose from. Many have lumbar supports and are designed to be ergonomic and comfortable.
Office chairs are also a status symbol. Typically, the higher ranking you are in a company the larger your office chair is, both in height and width. Regardless of your status, everyone who works a desk job uses an office chair and would be hard-pressed to continue their job without one.