Nico Diath was a Jedi Master of the Old Republic. A descendent of ancient and legendary Jedi Knights Sidrona Diath and Dace Diath, Nico Diath attained legendary status among the Jedi in his own time. The Force ran stong in the Diath family line as Nico was uncle to a young Jedi Knight, Tae Diath. Before the outbreak of the Clone Wars, Nico was somewhat of a maverick among the Order. Roaming the Outer Rim, beyond the jurisdiction of the Repubic, and technically the Jedi, Nico Diath roamed the systems freeing slaves and creating many an enemy among the Hutts. But Nico Diath felt that there were no boundaries to slavery and conducted himself according to what he felt was right.

Shortly after the outbreak of the Clone Wars, the Jedi Order discovered a sinister plot by the Separatists who planned to release a chemical weapon that intended to target and wipe out the clone troopers the Republic relied upon. An investigation led the Jedi to the planet of Queyta where the chemical was being manufactured. Chosen to lead the mission to obtain an antidote, Master Diath was joined by other legendary Jedi Masters Obi-Wan Kenobi, Knol Ven'nari, Jon Antilles, and Jedi Master Fay. On the bluffs of Queyta, a planet covered in rivers of molten rock, the Jedi gathered and discussed their plans for infiltration. Diath did not take it personally that Jedi Master Antilles informally took command of the mission and led the Jedi inside.

Making their way to the synthesis lab, the Jedi were surprised to find that they were beaten to the antidote by Separatist commanders Asajj Ventress and Durge who sought to obtain the sample for the exact purpose of preventing the Jedi from stealing it. Covering their escape with explosives, the initial blast claimed the life of Jedi Master Ven'nari. The explosion also damaged the complex so that it started to sink into the lava and cutting the Jedi's time with which they had to succeed.