Hm. Likely he's the king's spy-master/chief of intelligence, and there are other lords with similar titles: Lord My Arm, who is head of the military; Lord My Feet, who oversees and maintains roads/other forms of transportation; Lord My Stomach, in charge of agriculture. Can't think of any more off the top of my head, but I'm sure as it became more of a hereditary aristocracy type system and less of a meritocracy/job description type thing, you'd wind up with "Lord My Little Finger" and "Lady My Earlobe" and "Sir My Right Knee", which all sorts of fancy reasoning to turn what sounds like an insult into a bit of flattery.
...I kind of want to read a story set in the society, although I have no desire to write one myself. (Or inspiration; what I've written is actually slightly more than I've got.)