What is the name of the American businessman who betrays Indy in 'The Last Crusade'?

The American businessman who betrays Indy in 'The Last Crusade' is Walter Donovan.

Donovan initially appears to be a wealthy industrialist and a serious sponsor of archaeological research. After discovering a tablet containing clues to the Holy Grail, he recruits Indiana Jones to find both the Grail and Henry Jones Sr., who has disappeared while pursuing the same mystery. Donovan presents himself as a patron seeking knowledge and discovery.

His real motive is immortality. Donovan is secretly cooperating with the Nazis and wants the Grail's supernatural power for himself. Once the expedition reaches the Grail Temple, he demonstrates that his ambition has overcome any concern for history, scholarship, or human life.

Donovan's betrayal is especially memorable because it is revealed gradually. Indy first trusts the financial support behind the mission, then learns that Donovan and Elsa Schneider are aligned with the Nazi effort. In the final test, Donovan chooses the wrong chalice, drinks from it, and rapidly ages to death. The character was played by Julian Glover.