The Jjaro were an extremely advanced species or individual that disappeared from the Milky Way galaxy millions of years before the battle of Tau Ceti.

The Jjaro possessed high-quality cyborg technology, such as that used to create the S'pht,[1] a star-destroying weapon known as the trih xeem,[2] the ability to move entire planets by warping space around them, some form of time manipulation technology, and the power to imprison the W'rkncacnter.[3] [4] After their demise, much of their technology to fell into the hands of the Pfhor, while the S'pht'Kr used Jjaro technology to fold Lh'owon's moon K'lia out of their home system.[1]

According to Durandal, the Nakh were the last extant client race of the Jjaro. They rebelled against the Pfhor 6,000 years before the end of Marathon 2.[2]

It is possible that the S'pht mythical beings – Yrro and Pthia – were Jjaro.[3]