Daleth was a Vaskan ambassador in 2374 who engaged in trade negotiations with the crew of the USS Voyager. Shortly after that the Great War between the Vaskans and Kyrians started.
For centuries, it was believed that Captain Kathryn Janeway had started the Great War that nearly wiped out the Kyrian race. In the Kyrian interpretation of events, Daleth negotiated with Janeway, that in exchange for stabilizing a cyclic wormhole, Janeway was to find Tedran, the leader of the Kyrians. However, Janeway started to commit genocide using deadly biogenic weapons against the Kyrian race to make the leader bow down to Janeway. When Daleth protested, he was put in the brig. After Tedran was captured, he gave an "enlightened" speech to Janeway saying that what she did was wrong and unjust. Moments later, Ambassador Daleth was forced to witness Tedran and his aide's executions. Tedran cited Daleth for shaming both races.
Later, it was The Doctor who was able to prove that it was Daleth and Tedran who started the war, Daleth having committed the first act in the war by killing Tedran when he temporarily held Seven of Nine and another crew member hostage. The Doctor condemned Daleth's actions as having resulted in "a tragic, needless death". (VOY: "Living Witness")