He was born in System Loski, a star system near the Klingon-Federation border which had been cut off from Qo'noS and the rest of the Klingon Empire. In the mid-23rd century, he devised a plan, along with the system's military governor, Admiral Loski, to bioengineer Klingon warriors to more closely resemble humans, allowing them to infiltrate Starfleet ships and facilities. Having been physically altered himself, K'pril joined Commander Kor's troops in their face-off against Starfleet at Organia.
Despite this project's success, it was met with fierce opposition, particularly once contact between System Loski and the rest of the Empire was reestablished. A brief civil war broke out between imperial forces and those loyal to Loski, including K'pril. During Loski's final suicidal battle, K'pril built a lifeboat and left the ship, in stasis, in hopes of being picked up by a Federation vessel, and being able to die in hand-to-hand combat.
This lifeboat was not discovered until 2367, by the USS Enterprise-D. Though foeless, and terminally ill due to his genetic alterations, Lieutenant Worf reprogrammed a security training holoprogram to allow him to "escape" sickbay and die while in (simulated) combat.(TNG short story: "I Am Klingon")