Warren Keffer was a Human male, who by 2259 was stationed on Babylon 5 and was a member of Zeta Wing under Zeta Leader Ray Galus. Early in 2259, Captain John Sheridan, a hero of the Earth-Minbari War, took command of Babylon 5. Shortly after his appointment, the Minbari warcruiser Trigati, the crew of which refused to surrender at the end of the war and held a grudge against Sheridan, came out of hiding. The crew hoped they could force Babylon 5 to destroy them, allowing them to have some honor in death and perhaps even reignite the War. Keffer was involved in the standoff with the Trigati until Sheridan sensed he was being set up and refused to fire on the ship, calling on another Minbari cruiser instead. The Trigati was asked to surrender, but the crew set the ship on self-destruct. 
When the explorer ship, the Explorer class ship EAS Cortez was lost in hyperspace, Keffer was one of Zeta Squadron's pilots that participated in its search. Sheridan formulated a rescue plan, the key point of which was to create a chain of ships, so that each Zeta member was in range of the previous squadmate and this way avoided being lost. Such method was successful and the Cortez was found. However, a strange black starship suddenly appeared. Zeta Leader Ray Galus and Keffer, who were concluding the chain, collided with it. Galus died, but Keffer was lucky enough to survive, although his Starfury was badly damaged and began drifting in the hyperspace with no communication. With no other way to guide the Cortez back to Babylon 5, Keffer began shooting at the direction of the exit gate. Cortez's captain Jack Maynard understood Keffer and the Cortez returned safely along with the rest of Zeta Squadron. Keffer was presumed killed in action with Galus.
Keffer soon regained control of his ship, but the exit gate's signal was lost. Suddenly, the same strange object appeared. Thinking that it might have been travelling along the same course where Babylon 5 was, Keffer followed the ship and soon returned to the station. There, he was greeted and asked to become a new Zeta Leader. Keffer accepted the offer and soon reported about the mysterious ship. However, since his recording machinery was not working at the time of this encounter, he had noevidence to prove what he had seen. Following this, he became determined to find out what the spacecraft really was.
While Babylon 5 became a party to 25,000 GROPOS, Keffer was forced to share his quarters with two marines, Large and Yang. While Keffer was initially frustrated with such conditions, the three soon became good friends. Unfortunately, both marines were killled in Operation Sudden Death on Akdor shortly thereafter.
Short time later, an unidentified object was spotted near Babylon 5 and Keffer was sent to investigate. It turned out that the object was just a teddy bear—a toy which was made for the Babylon 5 fair to portray John Sheridan, and which was spaced out by Sheridan himself. Smiling, Keffer did not reveal what the object was, reporting only that it was harmless.
Keffer used much of his off-duty time looking for the mysterious ship that he had encountered in hyperspace. When this became known to the command staff, Keffer was ordered to stop. 
When a Markab transport vessel was delayed beyond an apointed time and was not respondng to Babylon 5's calls, Zeta Wing was sent to investigate. Keffer and his group soon found the ship drifting in space with the entire crew dead, killed by the "Drafa Plague".
Keffer soon received a word that one of Delta Wing's pilots, Mitch Harvey, had also seen something in hyperspace. Keffer told Mitch about his own encounter and was warned by him to not try to find the vessel. However, Mitch gave Keffer his data crystal with some readings on the mysterious ship.
That same year, a war between the Narn Regime and the Centauri Republic occured. The Narns were defeated and their military forces were almost decimated. One Narn ship requested sanctuary near Babylon 5 and Sheridan agreed. However, the Centauri soon learned about it and demanded that the ship was given to them, to which end they sent a battlecruiser. Sheridan refused and the Centauri began targeting the Narn ship. Since that ship undervent repairing and thus could not defend itself, Zeta Wing was called to assist. While Babylon 5 fought the Centauri cruiser, Keffer's squad escorted Narns through hyperspace.
Keffer soon picked up a signal similar to the one that Mitch had given to him. He set off alone to investigate. Keffer was finally successful in his quest as he saw the same black ship. He managed to record it and dump that footage before the ship attacked and killed him. The footage from his ship was found and released on the ISN soon afterward.
Despite the ultimate price that Keffer paid for this evidence, the footage was shortly removed from syndication. 
Keffer apparently had a wife or a girlfriend back home, from whom he received holographic messages.