In the anime and manga Mobile Suit Gundam universe, the MS-05 Zaku I was the first successful mobile suit design to be developed by Zeonic Company in the Principality of Zeon's quest to develop a combat-capable mobile suit that used the AMBAC System and the Minovsky ultracompact fusion reactor. The Zaku I was first designed and built in U.C. 0075, as the MS-05A Zaku. It wasn't put into mass-production until later that year, as the MS-05B Zaku I. The last production run of the MS-05B is in U.C. 0077, and was replaced by the newer MS-06 Zaku II unit.

The succsessful use of these suits prompted the Zeon Navy to commission ships that could carry them into combat, primarily the Musai-Class Light Cruiser. The Zaku I was already rendered obselete by the beginning of the One Year War by the Zaku II, and thus they were relegated for use in the rear lines as supply and construction suits. They still saw action, though, as colony gassers in the One Week War and towards the end of the war they once again saw frontline combat to reinforce the Zeon's weakening military lines.

A handful of these suits were upgraded during the One Year War for veteran and elite pilots who preferred the Zaku I over the Zaku II. There was MS-05S Zaku I Commander Type, which was used by mobile suit team commanders, and MS-05J Zaku I Land-Warfare Type, which was developed as a need for more mobile suits on Earth when MS-06J Zaku II Ground Type mobile suits were running low.