Ossu was an Ulk-Ra and warrior male of the Aelcluk. He was one of many individuals of warlike races abducted by the War Lords, who experimented on them to determine their suitability as soldiers in their armies. Eventually, the War Lords decided to use humans for their army.
Ossu-male was returned to his homeworld with a cybernetic implant that drove him to kill. He came across Coloth during his initiation; Coloth saw him as a beast as big as a fully grown Ulk-Ra alpha-male but covered in a thick pelt. The implant appeared as a strange glossy surface buried in the flesh of his head, as if a giant forest beetle had eaten its way into his face. Ossu-male subsequently killed Coloth.
Desperate to find his tribe, Ossu-male ate Issu-mul berries, to become a thinker like the female Ulk-Ras. Midway through hir transition to Ossu-female, hir was Ossu-hir, "not male or female, not suited for war or thought, or for land or sea". Ossu died burning at sea, from the waters, which were still poisonous to hir.
Zoe Heriot, upon examining hir body, was able to tell that Ossu seemed at once male and female. (PROSE: War Crimes)