Doctor Nel Apgar was a Tanugan scientist who appeared in the Star Trek: TNG episode, "A Matter Of Perspective".
In 2366, he developed a Krieger wave converter in his orbiting research station above Tanuga IV. The research was supported by the Federation and Commander Riker visited him to check on his progress. Apgar concealed the discovery from Riker because he decided to sell the Krieger wave as a weapon. Apgar's attitude plus his request for extra material so he could complete the weapon caused Riker to become suspicious of Apgar's intentions. Fearing he might be exposed, Apgar decided to kill Riker. As Riker was transporting back aboard the USS Enterprise-D, Apgar fired a Krieger wave at him, but 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.