Kim Jung-ju, the founder of South Korea’s biggest game maker Nexon and an engineer-turned-entrepreneur who led the country’s burgeoning game industry which also made him the richest man here, passed away on Monday. He was 54.

According to Nexon’s holding company NXC, Kim died on Feb. 28 in Hawaii, the United States. He had been undergoing treatments for depression and it appeared that the symptoms had become worse as of late, the company said.

Born in February 1968 in Seoul, Kim graduated from Seoul National University with a bachelor’s degree in computer science in 1991. After he received a master’s degree in the same major from the Korea Advanced Institute of Science and Technology in 1993, Kim founded Nexon in 1994.

Two years later, Kim’s Nexon debuted the world’s first massive multiplayer online role-playing game, The Kingdom of the Winds. The game introduced a new concept of interacting with other players in the game, working together to complete group quests and trading items among the players.

In the following years, Nexon released megahit titles such as MapleStory, KartRider and Mabinogi and Dungeon & Fighter on its way to become the largest game developer in South Korea.

The game developer went public on the Tokyo Stock Exchange in 2011. Following the listing, Nexon became the first Korean gaming company to surpass 1 trillion won ($830 million) in annual sales the year it went public.

Offering more than 45 games in 190 countries, Nexon still stands as the only Korean gaming company to post annual sales of over 3 trillion won, a feat it achieved in 2020.

As the game maker grew, Kim’s net worth skyrocketed. Last year, a report from the US think tank Institute for Policy Studies named him the country’s richest man with assets valued at $14.1 billion. According to Forbes’ list of Korea’s 50 richest published last year, he was number three with a net worth of $10.9 billion.

Kim established Asia’s first computer museum, the Nexon Computer Museum on Jeju Island in 2013. He helped build the country’s first rehabilitation hospital for children, which opened in Seoul in 2016. His company donated 20 billion won for the construction.

He went through a series of investigations by prosecutors for allegations of suspicious stock trading, bribery and tax evasion since 2016, but was eventually acquitted.

In early 2019, Kim tried to sell his entire stake in NXC, owned by him and his family, but pulled back from the sellout plan about half a year later. It was speculated that he could not find a suitable buyer.

The late gaming giant is survived by his wife and two daughters. The bereaved family has flown to Hawaii.

As Kim’s sudden death came as a shock, the gaming industry paid condolences to the late pioneer.

“It is difficult to express the tragedy of losing our friend and mentor Jay Kim, a man who had an immeasurably positive impact on the world,” said Nexon CEO Owen Mahoney, using Kim’s English name.

“As a founder and visionary leader, Jay encouraged those around him to ignore the skeptics and trust their creative instincts. He will be deeply missed by his Nexon family and many friends.”

Kim Taek-jin, CEO of gaming giant NCSoft, said the friend he loved has left.

“I feel the greatest pain I have not felt before in my life. My friend who walked on the path of life with me. I loved you. Rest in peace, please,” he wrote in a post on his Facebook account.