Sneakers was Ryan's old dog who died.
He met his demise when Ryan's sister let the gate leading to their pool open and he fell in and drowned. He was a gift to Kristen for one of her childhood birthdays but formed a strong bond with Ryan instead. Sneakers was so close to young Ryan that he often curled up with him and affectionately licked his face. Sneakers was known for his ability to perform backflips.
Sneakers may or may not have had an appreciation for Reebok Pump shoes and may have held a grudge against Kristen from beyond the grave - if Wilfred and Ryan's visions are to be believed.