The MS-04 Bugu (MS-04 ブグ?) is a mobile suit featured in the Mobile Suit Gundam: The Origin and Mobile Suit Gundam: The Origin MSD Cucuruz Doan's Island manga, the Mobile Suit Gundam: The Origin OVA, its television recut, and the Mobile Suit Discovery design series. Developed by Zeonic from the YMS-03 Waff , tests were conducted at the Dark Colony in U.C. 0077 . In U.C. 0078, Ramba Ral's Bugu fought in the Battle of Mare Smythii .

The development of the mobile suit took a huge step forward thanks to the compact fusion reactor and fluid pulse system designed by Dr. Torenov Y. Minovsky, resulting in the birth of the prototype YMS-03 Waff. The MS-04 Bugu was completed using data gathered with the Waff, and it was designed with a focus on its mobility, maneuverability, and ease of production as a weapon, making this the first machine capable of handling genuine combat. To improve its mobility, the power pipes that transmitted energy as part of the fluid pulse system were attached to the outside of its armor, and the increased supply of the energy used to drive its limb joints gave it very high maneuverability. However, as is often the case in the development of high-performance prototypes, it was designed with no regard for ease of production. With its high production cost, it was unsuited for mass production, and the role of official mass-produced machine was given to the redesigned MS-05 Zaku I. Though the Bugu never entered mass production, several units were built .