Bahbem is the financial backbone of Terra and the one who started it all. Though he may appear like a normal human being, Bahbem has been switching bodies for centuries. The Bahbem we see in the series is just a clone of the original Bahbem. At the end of the series he even switches bodies with his niece, Helena. Nobody can really tell what his age is exactly.
Originally from the Mulian world, he is largely to blame for splitting the world up in two thanks to his RahXephon project. The Mu continent completely disappeared from the face of Earth and moved into an alternate reality. The two worlds then become completely alienated when this split caused an impenetrable time-shift barrier to occur. From that moment on, Bahbem keeps studying his RahXephon project in hopes of one day joining the two worlds once again before they become a ball of mud. However, Bahbem has no preference as to who wins the tuning of the world, whether the Mulians or the humans as he even aids both parties. He's even indifferent as to how he uses people to achieve his goals. He's more obssessed over his project actually working, and in turn this obsession is what makes him such an arrogant and elitist "designer." The only thing that keeps him kicking is that he wants to see the tuning of the world with his own eyes. Unfortunately, he is shot dead just moments before the tuning by Lt.Col. Takeshi.
You can read more about Bahbem on Question #11 from the FAQ.