An Iyaaran ambassador aboard the Enterprise-D in 2370 who insists on Worf as his guide and sets out to be as offensive to him as possible.
Byleth appears in the seventh-season episode Liaisons. From the moment he arrives he is rude, demanding and contemptuous, rejecting Riker as his liaison in favour of Worf and then finding fault with everything the Klingon does.
Worf, ordered to be diplomatic, endures it with difficulty. At a poker game Byleth cheats openly and insults him, and Worf at last loses his temper. The two end up fighting in the holodeck for hours.
Byleth is thoroughly satisfied. His mission was to experience antagonism, which is unknown among his people, and Worf has given him an excellent demonstration. He thanks him politely and goes off to write his report. He was played by Michael Harris.