Put the diced onion on the bottom of the slow cooker.
Add the chicken on top of the onion.
Sprinkle the ranch seasoning mix and the pepperoncinis and the half cup of juices from the jar over the chicken.
Place the butter on top. (It will melt into the sauce during cooking)
Cover and cook on low for 7 hours or on high for 4 hours.
Serve the chicken thighs whole or shred them all. We like to serve this a variety of ways. Serve over rice, on burger buns with other sandwich toppings, over mashed potatoes, or we even like to use it as a burrito or taquito filling.