Why is it called Shepherd's Pie?

Where did the name for this tasty casserole come from? I'm just wondering how the name is tied to the fact that you basically throw all your leftovers in a baking dish and cover it in mashed potatoes and butter, toss it in the over, then scoop and enjoy. Did shepherds of long ago find peas, carrots, ground meat of some sort, corn, and mashed potatoes, and decide it was a novel idea to put it all together and heat up? Or did a person with the last name Shepherd devise the concoction because he needed to clean out his fridge, and the rest is history?

Regardless, I just made a fantastic version after having cleaned out my fridge. Delicious. Recipe as follows: layer sauteed italian-spiced ground turkey, variety of leftover veggies (corn, green beans, peas), throw in random spices, top with leftover mashed potatoes. Bake 350 degrees, 35-45 minutes. A delightful Shepherd's Pie will tantalize your taste buds. Who would have thunk that a combination of old fridge stuff can combine to make something so wonderful?

Warning: I wouldn't recommend doing this with left over chinese food, though...I don't think that's what the shepherds intended...