Siddhartha Gautama can be spelt at least 2 different ways. What are the different spellings and what reason is there behind it?

Siddhattha Gotama was his personal name before the enlightenment. His name Siddhattha means "He Who Attains His Goal" and Gotama was his family name. It was then changed to Siddhartha Gautama after the Enlightenment. Gautama simply means Buddha. It was changed since his disciples usually call him Buddha.

I am not sure if this is the answer but aside from Siddhartha Gautama, I think it can be Buddha. because this man was Buddha.