Arnie is a Pit Bull from the same organization run by James Woods, and the dog Barbara lost to. After the organization shut down due to Brian and Barbara testifying against James, Arnie was looking to strengthen up. Eventually, he fought Vinny. Sometime after, he was bitten by a wolf and cared for at the veterinary clinic after Barbara's daughter Briana found him and took him at said clinic. The two fell in love since, and Barbara eventually forgave and accepted him. He gave up fighting and found a new hobby in ventriloquism.
Wobbley on deviantART suggested he should wear a black collar with spikes on it and a round bronze tag.
Note: Family Guy is copyright of Seth MacFarlane and 20th Television Animation, a division of The Walt Disney Company. Arnie is a character originally thought up by hopeless-romance45 (Villains' Bad Girl), but I did the character design and currently own him.