In the films, Ron’s Patronus makes its official debut in “Harry Potter and the Order of the Phoenix” after a number of attempts during one of Harry’s training sessions with Dumbledore’s Army. While the Jack Russell terrier might not be the largest species of dog you’d want on your side, its very nature lines up perfectly with Ron’s, becoming a perfect ally to call into action. While very intelligent and always up for making themselves heard, Jack Russell terriers can be very stubborn dogs that will stand their ground against anything bigger than them.
Plenty of those traits present themselves in Ron throughout the series, not only holding his own against monumental odds but also sticking by those he cares about when things are at their worst, only reaching his breaking point in one of the “Harry Potter” franchise’s most heartbreaking moments. All dogs are loyal to those they care for, just like Ron is, but the Jack Russell terrier breed, in particular, is a perfect Patronus pairing. If anything, Ron’s terrier is the perfect display of that age-old saying: It’s not the size of the dog in the fight, it’s the size of the fight in the dog.