After making it past the three tests, "Breath of God", "Name of God" and "Leap of Faith", Indiana enters a small room with an old bent knight sitting and reading a Bible, a large table of gold grails behind him.
All but one of those grails, the Holy Grail, give whovever drinks of them death.
Donovan drinks out of one of them, and he turns into a skeleton. Who put the power to immediately kill into those grails?