Nintendo Entertainment System (NES)

From Geekcomix:

The Nintendo Entertainment System was released in America in 1985, after some limited success in Japan as the Famicom. Over the next few years, its user base would grow exponentially until the NES surpassed the Atari VCS/2600 peak set in 1982.6 As of 1990, there were over 19 million NES systems in the United States alone.5
In addition to the tremendous success of the system, its games had a great deal prosperity. For example, Super Mario Bros. 3 released in 1989 grossed over $500 million just in America. In the field of entertainment, only the movie E.T. has made more revenue.3 Super Mario Bros. 3 would sell more than 7 million copies in America and 4 million in Japan, which is more copies than any other game in history. Sheff wrote, "By record-industry standards, 'SMB3' went platinum eleven times. Michael Jackson is one of the few artists to have accomplished this feat."9
By 1990, the money earned from Nintendo's NES and its games allowed Nintendo to usurp Toyota as Japan's most successful company. In the entertainment business, Nintendo netted as much as all of the American movie studios combined, and more than the three television networks had in the previous two years. In the five short years since the system was released, the NES could be found in more than a third of the household in America and Japan. 9
This monopoly gave Nintendo significant control over the market during the Fourth Generation, which they utilized in various malicious schemes. Despite all of this, they are still one of the most popular and well-known companies in the world.
Nintendo's only competitor in the 8-bit market was Sega with their Sega Master System. While the Master System did have many more features than the NES (which is evident in a side-by-side comparison) it lacked the third party support that Nintendo had and was not much competition. The Master System sold a total of 2 million units and at times had a market share of 11%, these were the only reason the system survived as long as it did.