Ikegami Tsushinki, founded on September 10, 1946, is a manufacturer of broadcasting and communications equipment. In the late 1970's and early 1980's, the company developed arcade games for Nintendo and Sega.
According to the 2005 book Sore wa "Pong" Kara Hajimatta by Masumi Akagi, Ikegami designed and developed the arcade game Radar Scope for Nintendo. The game did very poorly, so then-Nintendo of America President Minoru Arakawa had Shigeru Miyamoto design a new game using the Radar Scope hardware - Donkey Kong. Programming was handled by Ikegami. 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 (by a company called Iwasaki Giken) and soon came Donkey Kong Junior (noted by Akagi 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 of 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 was merely Zaxxon with some tweaks).
- Block Fever (Manufacturer: Nintendo)
- Congo Bongo / Tip Top (Manufacturer: Sega)
- Donkey Kong (Manufacturer: Nintendo)
- Popeye (Manufacturer: Nintendo)
- Radar Scope (Manufacturer: Nintendo)
- Sheriff (Manufacturer: Nintendo)
- Space Fever (Manufacturer: Nintendo)
- Space Firebird (JP Manufacturer: Nintendo; US Manufacturer: Sega/Gremlin)
- Zaxxon (Manufacturer: Sega)