Roger Waters rejoined Pink Floyd for Live 8

Roger Waters.

The 2005 Live 8 show in London was the first time all four classic Pink Floyd members played together since Waters left in 1985. Gilmour and Waters had been feuding for years, but Bob Geldof convinced them to do it for the cause. They played four songs, and it was the last time they’d all be on stage together (Richard Wright died in 2008).

If you’re looking for the specific answer: yes, it was Roger Waters. He was the “former member” who came back.