Satoru Iwata, the company's president, has passed away at the age of 55, according to a statement issued by Nintendo. The cause of death was a bile duct tumor.
Iwata was named president of the company in 2002, when he succeeded Hiroshi Yamauchi. Iwata was only the fourth president in the history of Nintendo, and the first outside of the Yamauchi family.
Even while he rocketed up the corporate ladder, Iwata made clear that he was a gamer first.
"On my business card, I am a corporate president. In my mind, I am a game developer. But in my heart, I am a gamer," he said at a conference for game developers in 2005.
Under Iwata, Nintendo(NTDOF) cut ranks with other console makers, and sought to stretch the definition of "gamers." He rolled out the popular Nintendo DS and Wii platforms, along with games that appealed to more casual fans.
The DS was a clunky, plastic device that had two screens -- one a touchscreen, before that was trendy. It was going up against Sony's sleek PlayStation Portable, which was compared favorably to Apple's iPod. But the DS had games that appealed to casual gamers, like Brain Training and Nintendogs, and became a massive success.
Critics similarly doubted the Wii before its launch: It wasn't HD, it was cheap, it had a weird controller and a funny name. But the platform again exceeded expectations, becoming a key piece of the legacy Iwata leaves at Nintendo.
Tributes were immediate on social media, even from industry rivals.
"Thank you for everything, Mr. Iwata," the official Sony Playstation account tweeted. Another fansaid: "Good bye, Satoru Iwata. Thanks for speaking directly to our hearts."
Iwata briefly addressed his illness in 2014, when he wrote a letter to apologize for missing the company's annual shareholders' meeting.
"In general, it is said that a bile duct growth can be difficult-to-treat, partly because of the difficulty of detecting it early," he wrote. "In my case, luckily, it was detected very early and I had no symptoms."
Nintendo did not immediately announce a successor. The company said that two other executives -- Genyo Takeda and Shigeru Miyamoto -- would manage the company in the interim.
After opening higher on Monday, Nintendo shares trading in Tokyo quickly reversed course, losing 0.5%.
-- CNN's Ravi Hiranand and Yoko Wakatsuki contributed reporting.