The British East India Company was a joint-stock company formed in 1600 to conduct trade and commerce in the region of the Indian Ocean. The company was so successful that it actually ended up acting more like a sovereign nation than a company. The British East India Company seized control of large swaths of the subcontinent of India, colonized areas in Southeast Asia, and colonized Hong Kong following a war with China called the First Opium War.
Opium was a major driver of the trade and commerce that fueled the British East India Company. Other products included cotton, silk, indigo, dye, salt, spices, and tea.
Under control of the Qing dynasty, the Chinese made the import of opium illegal. With extremely high demand for silk, porcelain, and tea from China in Britain, the prohibition of opium suddenly created a vast trade deficit. In order to counteract this, Britain set up a vast smuggling network from India into China. By this point, the Chinese market was addicted to the drug and demand remained high. The East India Company, of course, wanted the profits from the opium trade, but also saw the opportunity to physically weaken the Chinese population through addiction.
As the import of opium continued to rise in the face of prohibition, the Qing dynasty placed the death penalty on opium smugglers. This led to a war between Britain and China in which Britain soundly defeated the China and colonized Hong Kong.