Parker is a minor character in Hotline Miami. Parker is an undead dog encountered during the outro of Crackdown in a hallucination. It is assumed that, just like every other hallucinated undead person, that Parker is one of the many dogs that Jacket has killed during his attacks on the Russian Mafia.
Parker is only ever encountered after Jacket is about to enter the pizzeria, where he is stopped by an undead Mobster warning him with "We don't like strangers around here, ain't that right Parker?" to which the dog responds with a low growl.