"If you were not an ambassador, I'd disembowel you here!"
– Worf, 2370 ("Liaisons")

Byleth was an Iyaaran ambassador.

In 2370, he and fellow ambassador Loquel came aboard the USS Enterprise-D as part of a cultural exchange with the Federation. The ambassadors were assigned to study two aspects of Human emotion, with Byleth studying antagonism and Loquel studying pleasure. A third ambassador, Voval, tested Captain Jean-Luc Picard on a class M moon in a study of love.

In his study of antagonism, Byleth participated in a tour of the Enterprise-D conducted by Lieutenant Worf. He was originally assigned Commander William T. Riker, but opted for Worf instead. Worf tried to resist antagonism at first, but eventually caved in. To his surprise, after snapping at Ambassador Byleth, Worf did not get reprimanded, as it was the culmination of Byleth's study. Later, Worf and Byleth spent eleven hours in holodeck battle exercises, during which they became friends.

The studies of Byleth and Loquel were both deemed a success. Voval, however, believed his experiment to be a failure. (TNG: "Liaisons")

Byleth was played by actor Michael Harris.
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