What was the final major expansion released for the original Destiny?

The final major expansion released for the original Destiny was Rise of Iron.

Released on September 20, 2016, Rise of Iron was Destiny’s fourth and last major expansion. Its story centered on Lord Saladin, the Iron Lords, and the return of SIVA, a self-replicating Golden Age nanotechnology threatening Earth’s survivors.

The expansion added the Plaguelands patrol area, the Iron Temple social space, new missions, weapons, armor, a Crucible mode called Supremacy, and the six-player Wrath of the Machine raid. It was released only for PlayStation 4 and Xbox One, unlike the earlier expansions.

A common mix-up is The Taken King, which was the third expansion and the largest earlier overhaul. Destiny later received the Age of Triumph update in March 2017, but that was a live update rather than a new major expansion.