In 2366, he developed a Krieger wave converter on the Tanuga IV research station. Supported by the United Federation of Planets, the method could prove to be a new power source. However, motivated to reward his wife for all the patience she had shown with him during his devotion to his work, he decided to sell the Krieger wave converter as a weapon to other organizations for a more profitable outcome. He therefore started ordering more dicosilium over several months in order to create larger reflective coils.
The Federation started having suspicions about Apgar's intentions and sent the USS Enterprise-D earlier than expected to report a status update. Commander William T. Riker and Geordi La Forge arrived on the station. Apgar concealed his discovery from Riker and attempted to explain away the need for the extra dicosilium. He further was angry at Riker over perceived advances on Manua, and accused him of holding the report over him if he spoke out about it. Fearing he might be exposed, Apgar decided to kill Riker and sent Manua and his assistant, Tayna, back to the Tanuga IV. As Riker was transporting back aboard the USS Enterprise-D, Apgar fired a Krieger wave at him, but, instead, the beam was reflected back into the station's main reactor by the transporter beam surrounding Riker and Apgar was killed when the station exploded.
His death and the station's destruction was investigated by the Tanugan authorities. Initially, Riker was accused of it, but after several accounts of the visit were studied, Apgar's motives and the cause of the destruction was revealed. (TNG: "A Matter of Perspective")