The Speaker in Destiny was killed by Ghaul during the Red War.
In the Destiny universe, the Speaker was a central figure in the Last City and a representative of the Traveler, the mysterious celestial body that gave Guardians their power. Throughout the first game and its expansions, the Speaker provided guidance and interpreted the will of the Traveler to the Guardians.
However, in Destiny 2, during the Red War campaign, the city falls under attack by the Cabal, led by their emperor, Dominus Ghaul. Ghaul seeks to harness the power of the Traveler for himself, believing that the Cabal are more deserving of its gifts. In the process, he captures the Speaker, seeking to force him to reveal the secrets of the Traveler.
The Speaker is held captive aboard Ghaul’s command ship, the Immortal, where he is interrogated. Despite being tortured, the Speaker maintains that he speaks for the Traveler but cannot summon it at will. Eventually, it is revealed that the Speaker has been more of a figurehead than an actual conduit for the Traveler’s will.
As the Red War campaign progresses, the Speaker is seen one last time in a cutscene where he confronts Ghaul, telling him that the Traveler will never speak to him. Shortly after this, the room they are in is shown in disarray, and the Speaker’s mask is seen on the floor, indicating that he has been killed during the Cabal’s occupation of the city.
The Speaker’s death marks a significant moment in the Destiny 2 storyline, as it leaves the Guardians without their long-standing spiritual leader and advisor. It also sets the stage for the Guardians to rise and take back the Last City without the guidance of the Speaker, relying instead on their own strength and the leadership of other key figures like Commander Zavala, Ikora Rey, and Cayde-6.