Tydinus Halcyon was a turian who served in the Citadel Council Navy, and became the first turian Supreme Commander of the Citadel Navy. He was regarded as the best military strategist in the navy, and despite the Turian Hierarchy's relatively recent entry into the galactic community, rose to a position of power.
Halcyon served in the Turian Defense Force for many years, where he demonstrated his brilliance. However, many of Halcyon's tactics and strategies were controversial due to the brutality inflicted upon enemy combatants, and the fact that they involved a mobile form of warfare, very different from the accepted Turian strategies of static warfare, and so he was kept from advancing above the rank of Rear Admiral. Upon the Turian Hierarchy's contact with the Citadel Council and its joining of Citadel Space, Halcyon was recruited into the Citadel Navy, who introduced him to the salarian councilor. The salarian councilor approved of Halcyon strategies as a viable way to end the Krogan Rebellions.
Over time, Halcyon climbed the Citadel Navy ladder, and eventually became the first turian Supreme Commander of the Citadel Navy. Shortly after, Halcyon left on a secret mission to oversee the research and development of the Genophage, a disease that would hamstring the krogan ability to fight by reducing their number of births to pre-industrial levels. He remained there for several months, and when he returned the Citadel Council was on the verge of collapse. He had a plan to crush the Krogan Union. Though the Supreme Commander was able to deal the Krogan Union several mighty blows, he was unable to destroy the insurgent government. Halcyon decided to release the Genophage on the krogan, who had begun a push towards the Citadel, reducing their ability to fight. After the krogan ranks were decimated, Halcyon led the clean-up campaigns against the Krogan Union's remnants before being assassinated by disgruntled krogan.