Ikegami Tsushinki (池上通信機), founded on September 10, 1946, is a manufacturer of broadcasting equipment. In the late 1970's and early 1980's, the company developed arcade games.
Among those games was Radar Scope, which Ikegami designed and developed for Nintendo.  The game was popular shortly in Japan, prompting Nintendo of America President Minoru Arakawa to place a large order for it. But by the time units reached the States, any buzz surrounding the game had dissipated and arcade operators were left unimpressed. Facing financial disaster, Arakawa asked his father-in-law and Nintendo CEO Hiroshi Yamauchi to provide him with a game that could be installed as a replacement. 
Yamauchi assigned a young Shigeru Miyamoto with designing a new game using the Radar Scope hardware. What Miyamoto came up with was Donkey Kong. Nintendo decided to work with Ikegami, which had the technology to program it. Ikegami wrote all the code and sold Nintendo 8,000-20,000 PCBs (Nintendo copied 80,000 without permission). Since there was no contract between Ikegami and Nintendo, Nintendo did not have the source code. But Nintendo wanted a sequel, so DK was disassembled and reverse engineered (through subcontractor Iwasaki Giken) and soon came Donkey Kong Junior (noted as being the first Nintendo game developed entirely in-house). In 1983, an angered Ikegami sued Nintendo for ¥580,000,000 for copyright infringement, claiming it owned the original DK code. In 1990, the two companies settled out of court. The details of that were not released to the public. In another trial that year, it was determined that Nintendo did not hold the copyright to the DK code. 
If you look at the tilesets from some of the games listed below, you will find the Ikegami logo (see right).  It shows up in Congo Bongo, Donkey Kong, and Zaxxon. It also turns up in Donkey Kong Junior and Super Zaxxon, but it is unknown if Ikegami was actually involved with the latter (the situation with DK Junior was explained earlier; Super Zaxxon is essentially a more challenging version of Zaxxon). It is also unknown if Ikegami was involved with Future Spy, a conversion for Zaxxon.
- Block Fever (Nintendo)
- Donkey Kong (Nintendo)
- Popeye (Nintendo)
- Radar Scope (Nintendo)
- Sheriff (Nintendo)
- Space Fever (Nintendo)
- Space Firebird (Nintendo)
- Tip Top / Congo Bongo (Sega)
- Zaxxon (Sega)
- 1. Sore ha Pong kara Hajimatta: Arcade TV Game no Naritachi, Masumi Akagi, Amusement Tsuushinsha, 2005.9, ISBN 4990251202.