i think that both of gotama and siddharta represent the concept of illumination , wich could be claimed in many ways , i think that hesse used those 2 names in order to show the difference of pathes , and to say that each person should repsect the other point of view , and the other ways of seeing stuff .... and thus life is a libre arbitre where you experiment ,and it s the choices that yuo make that will guide you to your goal , there s no WAY to arrive there , each person should addapt himself to his situation adn to the goal he s seeking in order to get there
i just want you people to excuse me for my poor english , but i think that my idea is clear

Buddha , before attaining enlightment was known as Siddharta. Buddha is not a name but a state of Nirvana. Thus siddharta in this book only symbolises a character .

yes in the book, they are 2 people. this is intentional I believe because in Budhism, there is the self that simply experiences and the self that knows of the experience. The book explores this by splitting up the two into seperate characters.

this theme is also present in Narcissis and Goldmund

You hit the nail on the head - "Novel".

I am a high school student, and from my religion class studies i can tell you that yes, Siddhartha Gautama (only one among the many spelling versions) is the same person as the Buddha. According to the myth, Siddhartha Gautama was born as a son to a military ruler of an Indian region. The priests/oracles/or just wise men, have told the father that his son is predestined to either be the ruler of the world, or its saviour. The king did all in his power to insure that Siddhartha does not astray from his perspective future as the ruler of the world, and therefore isolated him within the castle from all of the markings of suffering in life (decrepitude, sickness, death and a fourth one - those are known as the four passing sites). Any how, where was I. Oh yes,Siddhartha even got married and had a son. But during one of his outside of the castle strides through the city, the father's servants failed to succesfully realize their mission of hiding the old and the sick away from Siddhartha's itinerery, and he finally faced his destiny of encoutering the four passing sites , as already mentioned. Then he realized that life is not as perfect as he was brought up to belive. He joined the ascetic monks, and so on, and finally, after a couple of days spent in deep mediational trans, he "awakened" into Nirvana (the state of eternal bliss, being and awareness)....you do know that Buddha means" the awakened one"?
To try to answer to your main question : Why does Hesse makes those two aspects of Buddha's life into two separate characters? , I would have to recall the explanation that my teacher gave to me. The sad thing is that the only thing i can remember about it, is that it was a rather satisfactory and substantiated explanation. I'll ask about it on monday and let you know, if you're still ionterested.
Also, for my English class , i am about to read "Narcisus and Goldmund", so I'll report on that too... : - )

Gotama Siddhartha was the Budda's full name before he became the Buddha. The Siddhartha of the book is a different person altogether.

Thankyou for the information that you do not have, but hopefully will receive. Should I hold my breath O wise one.

I think that one of Hesse's possible intentions in giving the main character the same name as the Buddha was to illustrate one of the themes of the novel; that knowledge or enlightenment cannot be gained by following another, or even by learning from them, but only by personal encounter and experience. Thus, when Siddhartha and Buddha have their conversation, Siddhartha declines to follow the Buddha despite his high regard for him. The point is, that Siddhartha is the Buddha, but he is his own Buddha, not merely a follower of another.

sidartha is the his giving name and buddha is after he reach enlightenment.