The only intelligent alien life ever encountered by humanity was the array that attacked and destroyed the insurgent colony of Korpi in the Xylon system. It was this that led to the formation of the centralised Unity government.
It is not known what form the aliens take, the only contact being with the hostile array. Xenobiologists have theorised that the array itself may in fact have been the alien life itself, and certainly this idea is justified by the discovery that its detachable laser-pod weapons were biological in nature. However, a leading rival theory is that the array was simply an advanced biological weapon sent out to clear potential threats before a colonisation expedition.
The alien threat was defeated in the Battle of Tortuga in U10, and no other verified reports have been recorded since. Though Navy forces in the Galactic South West remain vigilant, it is thought that humanity has seen the last of these hostile beings.