In Destiny lore, Riven was the last Ahamkara to be killed. Riven of a Thousand Voices was a wish-granting dragon who served Mara Sov and the Awoken in the Dreaming City.
The Vanguard’s Great Hunt drove the Ahamkara nearly to extinction, but Mara secretly preserved Riven as a powerful asset. Oryx later Took her, and she eventually became a major threat in the Dreaming City. In Destiny 2: Forsaken, Guardians defeated Riven in the Last Wish raid.
Riven’s death was not a simple victory. The Guardians’ collective desire to save the Dreaming City fulfilled Riven’s final wish, allowing the Taken curse to trap the city in a repeating three-week cycle. Her spirit later returned during Season of the Wish, where she helped the Guardians pursue the Fifteenth Wish.
Riven is often called the “last known” Ahamkara because later stories revealed surviving eggs. Those eggs do not change the canonical answer to this question about the last Ahamkara killed.