Chinese consumer electronics manufacturer, a subsidiary of Oppo
OnePlus Technology (Shenzhen) Co., Ltd. (Chinese: 一加科技; pinyin: Yījiā Kējì), doing business as OnePlus, is a Chinese consumer electronics manufacturer headquartered in Shenzhen, Guangdong, China. It was a subsidiary of BBK Electronics, a company which also had Oppo. OnePlus was founded by Pete Lau and Carl Pei on 16 December 2013 to develop a high-end flagship smartphone running Cyanogen OS that would come to be known as the OnePlus One. OnePlus would continue to release smartphones afterwards.
https://en.wikipedia.org/wiki/OnePlus