Twenty-five years ago, when I started my fieldwork on the behavior of juvenile common octopuses in the azure waters of Bermuda, I expected all my subjects to be much the same. I assumed their activities would be fairly limited; individuals would hunt, rest, and avoid predators, all in roughly the same way. In fact, I learned, their behavior is quite complex and variable. I watched as they carefully chose rocky crevices for their dens and blockaded the entrances with piles of rocks. I observed them navigate complicated routes across the sea bottom to and from their hunting grounds. But I was most intrigued to discover that individual octopuses are very different from one another.could swear, for instance, that octopus number 45 never left its crevice–except that the discarded shells of clams, crabs, and snails kept appearing in front of the crevice. It must have been making secret hunting forays when my back was turned. By contrast, octopus number 26 was anything but shy. One afternoon I watched it as I floated in the shallow Bermuda water, hanging on to a rocky outcrop. The little octopus peered back at me from inside its den for some time, then suddenly jetted three or four feet directly toward me and landed on my dive glove. After about a minute of exploring, it must have decided the glove didn’t taste good, and slowly jetted back home. I was hooked.Around the same time, Roland C. Anderson, a marine biologist at the Seattle Aquarium who has since become my frequent collaborator, noticed that aquarium workers gave names to only three kinds of animals in their care: seals, sea otters, and giant Pacific octopuses. The workers named the octopuses for their distinctive behaviors. Leisure Suit Larry, for instance, was all arms. He touched and groped his keepers so often that had he been a person, he would have been cited for inappropriate behavior. Emily Dickinson, by contrast, hid permanently behind the artificial backdrop of her display tank, so retiring that eventually she had to be replaced by a more active octopus for aquarium visitors to watch. Then there was Lucretia McEvil, whose caretakers were afraid to approach her, and who ripped up the interior of her tank. All those “characters” set me to thinking about whether octopuses might just have something like human personality.

Twenty-five years ago it was hard to know what to expect of octopus behavior: the creatures had seldom been studied, and when they had, it was mostly in captivity. Furthermore, they are invertebrate mollusks, and so they are evolutionarily distant from vertebrates; it would have been hard to justify extrapolating the significance of their activities from the well-studied behaviors of mammals and birds.

Most mollusks are clams or snails that hide within hard shells and have little brainpower. But cuttlefish, octopuses, and squid (which along with nautiluses make up the cephalopod mollusks) are nothing like their shell-bound relatives. Evolution led them to lose their protective shells, but what they gained was far more interesting: dexterous, sucker-lined arms; ever-changing camouflage skin; complex eyes; and remarkably well-developed brains and nervous systems. The 289 known species of octopus range in size from the one-ounce Atlantic pygmy octopus, Octopus joubini, to the giant Pacific octopus, Enteroctopus dofleini, which can weigh more than a hundred pounds. They are all ocean-dwellers, and, though the group is distributed from the poles to the tropics, octopuses are reclusive beasts; individuals are hard to find, let alone study.

The intelligence of octopuses has long been noted, and to some extent studied. But in recent years, research by myself and others into their personalities, play, and problem-solving skills has both added to and elaborated the list of their remarkable attributes. They turn out to be uncannily familiar creatures, not nearly as unlike you and me as one might expect–given their startlingly different physiques and the 1.2 billion years of evolution that separate us from these eight-armed marvels of the sea.

Personality is hard to define, but one can begin to describe it as a unique pattern of individual behavior that remains consistent over time and in a variety of circumstances. I’ve adopted the model that developmental psychologists have applied to study the behavior of children. Psychologists begin with the idea of “temperament,” or behavioral tendencies genetically programmed before birth. After birth the environment shapes an individual’s temperament to give rise to an adult personality.