Prepare the ingredients. Gather the chicken breasts, Buffalo wing sauce, dry ranch dressing mix, butter, and hoagie rolls.
Add the chicken to the slow cooker. Arrange the boneless, skinless chicken breasts in the bottom of the slow cooker, spreading them out as evenly as possible.
Add the Buffalo sauce and ranch seasoning. Pour ¾ of the Buffalo wing sauce over the chicken, reserving the remaining ¼ for serving. Sprinkle the dry ranch dressing mix evenly over the chicken.
Slow cook the chicken. Cover the slow cooker and cook on Low for 6–7 hours, until the chicken is fully cooked and tender enough to shred easily. The chicken should reach an internal temperature of 165°F (74°C).
Shred the chicken. Use two forks to pull the chicken apart directly inside the slow cooker, allowing the shredded meat to mix with the Buffalo sauce and cooking juices.
Stir in the butter. Add the butter to the shredded chicken and stir gently until melted and incorporated into the warm sauce.
Prepare the hoagie rolls. Split the hoagie rolls lengthwise, keeping them connected on one side if preferred. Arrange them on a serving platter or individual plates.
Assemble the sandwiches. Spoon generous portions of shredded Buffalo chicken into each hoagie roll, dividing the mixture evenly among the six sandwiches.
Add the remaining Buffalo sauce. Drizzle the reserved Buffalo wing sauce over the sandwiches or serve it on the side so everyone can adjust the heat.
Serve warm. Enjoy immediately while the chicken is warm and juicy. Add blue cheese or ranch dressing as an optional topping.