Got it. My boy Jo is a 100 lb American Bulldog and he HATES other dogs. Our cats(yup, plural, ugh…) he tolerates. Never had a dog aggressive dog before Jo. My last American Bulldog was 140 lbs and loved playing with other dogs. He would lay down and let puppies at the ‘dog park’ wrestle and nip at him. If the my got out of line, he’d get up and give them his look and they would calm down. I used to walk him of leash thru soccer fields near our house even with soccer games going on. He never bolted after anyone and stupid parents would let their kids hang off of him.
Ivan sounds like an excellent candidate to be featured on Cesar Milan’s new dog socialization show. Ivan’s backstory of being run over and his recovery would be a storyline.