Who started creationism?

Answer:God started it on day one of creation. Mankind has believed it from the beginning of creation, since man was there and a part of it. Adam and Eve know the story to be true. A more appropriate question would be "Who started the idea of evolution?" because that is a fairly new belief. You will not find any writings as old as The Bible that teach evolution. AnswerMost anthropologists agree that religiOSity (and creationist stories) began sometime around 50,000-200,000 years ago, although it might have been quite a bit earlier but that is when the first good evidence for religion appears. Every culture since has attempted to explain their existence by invoking a different version of creationism. AnswerIf you are referring to the modern young earth creation movement, then the book, The Genesis Flood, by the late Dr Henry Morris and Dr John Whitcomb in 1961 was an important starting point. Dr Morris has been called the father of the modern creation movement.
Creationism has existed in some form for around 6000 years, as per the records of Jewish and then Christian society. In its modern form, creationism sprung up around the same time as evolution, as a response to defend against what was seen as a threat to their faith.

The people who developed both are either not known in the first case, or many and varied in the second.