Much of that work involved needing an ultramarathoner’s worth of exercise, but that kept the IPAs from adding territory to my gut. Krypto also herded other animals and sometimes people, did some occasional protection detail and set the stage for us becoming a family.

The other great work of his life was teaching. He taught my wife and me how to be parents, and he taught our sons the joys of unstructured play and the art of observation. Like Albus Dumbledore, he did his greatest educating in old age, showing our family how to live with infirmities and without self-pity, and in the end, how dying and dead are different things.

My wife, Sarah, and I believed that Krypto was the first great thing we did as a couple. The rescue outfit described the Australian cattle dog-mix puppy as “not much to look at and getting picked on by the other dogs because he was kind of a jerk.”

And he was indeed a hammerhead, early on escaping our yard and chasing a high school cross-country team until he caught the slowest kid. But he quickly responded to training and copious exercise. Krypto explored the north Georgia woods with us and was a witness to our engagement on the Benton MacKaye Trail. His squared-away self convinced us that we were qualified to repeat the experiment; this time with very small humans.

The pee on the pregnancy-test stick wasn’t dry before Krypto relocated his sleeping spot from the dog bed by my nightstand to the floor next to Sarah. He did the same thing when Donovan’s brother, Tate, came around two years later.

The books about dogs and babies urged us to bring a blanket home from the hospital so Krypto could familiarize himself with Donovan’s scent, followed by Donovan. Krypto was unimpressed.

Although Krypto was outwardly ambivalent, each time Sarah got up to nurse, he followed, sitting at her feet and facing the door, acutely keyed in to her vulnerability. He did so again with colicky Tate 2½ years later. The dog was working harder than ever but the boys moved him down in the pack order, just by virtue of being humans.

The transition from stinky, furious blobs to menacing, pokey toddlers to boys who just wanted to throw a ball or Frisbee all day long took dozens of dog years. Along the way, Krypto took down a prowler who came into the house while Sarah was upstairs reading to the boys. The perp was begging for mercy when I got to him, but Krypto greedily held his ankle. Good boy.

Not long after Donovan and Tate became full partners with Krypto, his interest in athletics began to wane. Cattle dogs tend to slow down around age 13 or so. We had a soft old couch that he’d made his own, and the boys liked to bounce on it and wake him for belly rubs or ear scratches. One day their protector snapped hard at them. He was sleeping more deeply and waking up anxious. It shook us up, but the boys were made aware that not everything in life can go at their speed. A little Prozac in Krypto’s kibble helped, too.

Krypto’s decline was the one we’re all hoping for: small increments over an extended period preceding a rapid crash, followed by permanent sleep. My sons received regular lessons in patience. Walks took a while so we had to leave earlier for school. Smell became more important to Krypto than locomotion, so the boys came to understand that a walk often meant standing around while he sniffed the world.

Krypto died with the lab work of a puppy; neurological failings were his undoing. Eventually, his front and back halves had trouble communicating, and he moved like a firetruck tiller with no one driving the back end. He needed help down the three steps to get outside. Cue my sons. They listened for Krypto by the door and were always ready to help him outside and wait patiently for him to find just the right spot before assisting him back up the stairs.

There were the requisite indignities and accidents. The boys helped him up and fetched the paper towels. “Krypto never seems to feel sorry for himself,” Tate said one day while doing exactly that over a pile of crap in the hallway. My sons were paying attention to these lessons.

In his last week, Krypto’s mobility cratered and his anxiety resisted the strongest tranquilizers. He kept us up half the night telling us it was time to let him go. I wanted him to die on his own terms but his mighty heart would not quit. Donovan and Tate heard their father blubber his way through explaining what would be our last measure of devotion.

(The surreal experience of watching one’s father cry uncontrollably has been compared to the first time you see Grandma in a bathing suit.)

Krypto taught my boys to accept decline and mortality, so they had no questions for our vet when she arrived with full eyes. The boys were with Krypto on the porch as the vet eased him from his mortal coil. They are different kids and handled the intense emotions in their own ways, but they were present, holding that dog as he left us, telling him how much he’d be missed.

They fell in love with a dog and, as the contract states, they had their hearts broken. They are better people for knowing him, loving him and losing him.

And in the end, my young men carried Krypto from the house for the last time. I have never been sadder or prouder.

Mike Mikula is a cartoonist and writer living in Atlanta.

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