Theoden King

Where does Theoden rank among the characters in The Lord of the Rings?  He is a king, certainly, but in many ways he is also at the mercy or whim of other, more important, characters.  Aragorn, Gandalf and Saruman all seem to direct his doings.  Even Grima, a mostly worthless person, has his way with Theoden.  One must then ask why he deserves the great honors he receives.  The answers are as complex as the times he found himself living, and to have simply survived and to have done so on the right side is certainly worthy of recognition.