what is the motivation of Shimura variety?

Tonight, a friend of mine give me a concise introduction to Shimura variety . I only get some first impression of it. I think the hodge structure is a generalization of the cohomology ring of Kaehler manifold or algebraic manifold , and i think of the Shimura variety an anologue of the analytic familly of complex manifolds , just as introduced in Kodaira's book Complex manifolds.And i suspect that there maybe some anologue theorem's as what Kodaira had done by deformation of complex structures . I'm just doing some imagination unboundedless , do not laugh at me !Heh!

-
We had a similar question at mathoverflow.net/questions/14175/… – S. Carnahan Apr 10 '10 at 16:13
I believe the main original motivation was Hilbert's twelfth problem en.wikipedia.org/wiki/Hilbert's_twelfth_problem – Dror Speiser Apr 10 '10 at 19:48

Shimura varieties are certain moduli of Hodge structures; but that is perhaps not the best point of view to understand why people study them. Rather, the primary motivation is the following: Shimura varieties are attached to (certain) reductive linear algebraic groups over $\mathbb Q$, and the geometry of the Shimura variety is closely linked to the theory of automorphic forms over the corresponding reductive group.