The story
The firm began in 1974 participating in Hyeopseong Industry. In 1985 Seoul Chemical was established. In 1996 the company was renamed from Seoul Chemical to Sonokong. In 2016 the firm's exclusivity agreement with Takara Tomy expired. Twelve percent of the company was sold to Mattel.
From Wikipedia’s article on Sonokong, shared under CC BY-SA 4.0.4