Combine the onion, tomato paste, oil, chili powder, garlic, and cayenne in a microwave safe bowl. Microwave about 3 minutes, until onion is softened, stirring occasionally.
Transfer to slow cooker and whisk in the ketchup, molasses, mustard, and vinegar. Season chicken with salt and pepper, arrange chicken in the slow cooker, and spoon sauce over top. Cover and cook on low for 5 hours, until easily pulled with a fork.
Transfer to a cutting board and cover with aluminum foil. Let rest for 15 minutes.
Whisk hot sauce and liquid smoke into the remaining sauce, cover and keep warm.
Discard skin and bones from chicken. Shred the chicken and return to slow cooker. Toss with sauce.