It is a relationship built on extraordinary confidence -- perhaps, even some blind faith.
"These guys are well over a ton," says Dave Salmoni, a large animal expert for the television network Animal Planet. "They can run about 35 miles per hour, which is faster than a horse. And you picture that coming at you, it's like a small car but worse, because this has horns."
Salmoni, who has worked with bison at Yellowstone National Park, where they have attacked and injured twice as many people as grizzly bears over the years, came with ABC News' "20/20" to meet Wildthing for insight -- and for our protection.
"Bison react aggressively to things that they are scared of," Salmoni says. "That just means you've got a humongous animal with horns and knows how to use him. He's going to start throwing you around."
But RC, 61, doesn't avoid taking this bull by the horns. He has spent his entire career as a rancher and rodeo clown, learning the crucial skills of how to handle fear and to roll with the punches. And there have been many over the decades.
"When I was 14 years old, a horse knocked my teeth out. I've had a huge amount of broken ribs and broken shoulders. I had my neck broke twice, and never missed a day's work," says RC.
Few others would choose to risk even more serious injury by living with a horned relic from the dinosaur age. Yet, RC never has shied away from being close to Wildthing. In the scorching heat of a Texas summer, the unlikely pair can be found swimming together in a nearby pond.
So how exactly did RC befriend the largest land animal in North America?
"I got him bluffed," he says. "And that's all there is to it. He's just bluffed. He doesn't attack me for two reasons. He thinks I'm tougher than he is, probably. But the bigger reason is that he loves me."
Love may just be the ace in the hole. Somehow, Wildthing knows to leave his wildness at the welcome mat.
"He's never been bad inside here," RC says. "Tears up everything outside and doesn't tear up anything in the house. One time, he picked up a couch and moved it. I told my wife she probably had it in the wrong place anyway! I would rather have him be in here than my kid most of the time."
Wildthing may be a well-behaved bull in a china shop, but RC knows that raising a bison as part of the family takes a special breed of human.
"Don't take a day off. It's seven days a week and it's three or four times a day," says RC. "I've never tried to make him a super gentle animal cause I enjoy him being wild. I want him safe for me, and I sure don't want him hurting anybody else. But I enjoy his wildness."
RC has enjoyed crossing nature's divide. And there is no returning after a lifetime of extraordinary and seemingly impossible feats.
"Matter of fact, I may be nuts and it may be exactly why I'm doing this!" says RC. "It's strange in your world, but it's not strange in mine 'cause I've lived with animals for 40 years."
When it comes to outrageous family members, Melanie Typaldos of Buda, Texas, understands that love comes in many sizes and species. She is the proud owner of Caplin, an unlikely entrant on the giant spectrum.
Caplin weighs more than 100 pounds, which may not seem noteworthy compared to a 2,100-pound bison, but is enormous when you hear what he is: a capybara.
"Capibaras are the world's largest rodents," says Typaldos.