Novel series of 4 books about a spy being cloned - 1 to breathe in water, 2 others were other types (sulphur or?) for 4 planet system about to break out into war. I read the series in the early 1980's borrowed from the local library in Australia so likely to be well a known author. Each book started off with spy thinking he is the original Terra style whereas in 3 he clearly is not.
It could be - Four Lords of the Diamond by Jack Chalker
The Confederacy, a massive space empire, duplicates the personality of its best agent and implants it into four brain-dead hosts. These hosts are sent to the four planets of a penal colony, the Warden Diamond, to investigate an alien threat and assassinate the four lords of the planets, the "Four Lords of the Diamond." The original agent is on a picket ship and downloads information from his copies.
Cerberus is the water world of the Warden system. In its dense jungles only the most ruthless survive. If Qwin, the Federation's finest operative is to survive and take over the mind of it's evil lord, he must exchange his body for that of a man (right now he is a woman, but don't ask.) and do it fast!
- Charon (1982)
They took the body of Park Lacoch, put in it the mind of a top confederacy operator and then stuck him aboard a spaceship bound for Charon - one of the worlds of the Warden Diamond, a hell-world from which there was no return.
- Medusa (1983)