Craig Packer was behind the wheel when we came across the massive cat slumped in the shade beneath a spiny tree. It was a dark-maned male, elaborately sprawled, as if it had fallen from a great height. Its sides heaved with shallow pants. Packer, a University of Minnesota ecologist and the world’s leading lion expert, spun the wheel of the Land Rover and drove straight toward the animal. He pointed out the lion’s scraped elbow and a nasty puncture wound on its side. Its mane was full of leaves. From a distance it looked like a deposed lord, grand and pitiable.
Since arriving in Tanzania’s Serengeti National Park only that morning, I’d gaped at wildebeests on parade, dawdling baboons, gazelles rocketing by, oxpecker birds hitching rides atop Cape buffaloes, hippos with bubblegum-colored underbellies. The Serengeti usually dazzles first-time visitors, Packer had warned, making us giddy with an abundance of idyllic wildlife straight out of a Disney song-and-dance number.

The sublime brute only 15 feet away was my first wild Panthera leo. Male African lions can be ten feet long and weigh 400 pounds or more, and this one appeared to be pushing the limits of its species. I was glad to be inside a truck.
Packer, though, opened the door and hopped out. He snatched a stone and tossed it in the big male’s direction.
The lion raised its head. Its handsome face was raked with claw marks.
Packer threw another stone. Unimpressed, the lion briefly turned its back, showing hindquarters as smooth as cast bronze. The beast yawned and, nestling its tremendous head on its paws, shifted its gaze to us for the first time. Its eyes were yellow and cold like new doubloons.
This was one of The Killers.
Packer, 59, is tall, skinny and sharply angular, like a Serengeti thorn tree. He has spent a good chunk of his life at the park’s Lion House, a concrete, fortress-like structure that includes an office, kitchen and three bedrooms. It is furnished with a faux leopard-skin couch and supplied only sporadically with electricity (the researchers turn it off during the day to save energy) and fresh water (elephants dug up the pipelines years ago). Packer has been running the Serengeti Lion Project for 31 of its 43 years. It is the most extensive carnivore study ever conducted.
He has persisted through cholera outbreaks, bouts of malaria and a 1994 canine distemper epidemic that killed off a third of the 300 lions he’d been following. He has collected lion blood, milk, feces and semen. He has honed his distressed wildebeest calf call to get his subjects’ attention. He has learned to lob a defrosted ox heart full of medicine toward a hungry lion for a study of intestinal parasites. And he has braved the boredom of studying a creature that slumbers roughly 20 hours a day and has a face as inscrutable as a sphinx’s.