Whenever dharma declines and the purpose of life is forgotten, I manifest myself on Earth.
I am born in every age to protect the good, to destroy evil, and to reestablish dharma.

In this quote from the Bhagavad Gita, it is Krisna who is speaking.  Krishna is another name for Christ and, as this short statement says, there have been many Christs who have come at different times and to different people when needed.  Jesus was Christ, to be sure, but that doesn't mean, as most Christians believe, that he was the only Christ.  Buddha, Joroaster and some other great prophets were also incarnations of the Christ Spirit.  An interesting note:  according to my readings, Krishna is considered an incarnation of Vishnu and Vishnu is also known as the Divine Sun.