But now, solid evidence has emerged of the dolphin's altruistic nature. In a act of selflessness which has astounded experts and confirmed the friendly nature of the species, a bottlenose came to the rescue of two whales stranded on a beach in New Zealand.
The dolphin – nicknamed Moko by local residents, who said it spent much of its time swimming playfully with beachgoers – helped two pygmy sperm whales, facing imminent death after becoming stranded on a sandbar, swim to safety.
Until Moko's arrival, rescuers feared the mother and calf would have to be put down to prevent them suffering a prolonged death on Mahia beach, about 300 miles north-east of Wellington.
Malcolm Smith and his team from the New Zealand Conservation Department had tried in vain to rescue the animals for an hour-and-a-half. With their effort faltering, it seemed only a matter of time before the operation was called off.
"They kept getting disoriented and stranding again," Mr Smith said yesterday. "They couldn't find their way back past (the sandbar] to the sea."
Just as it seemed all hope was lost, Moko appeared. The dolphin approached the whales, leading them 200m along the beach before navigating them out to the open sea.
Mr Smith believes the dolphin heard the whales' distress calls and came to their aid.
"It was looking like it was going to be a bad outcome for the whales ... then Moko came along and fixed it," he said. "They had arched their backs and were calling to one another, but as soon as the dolphin turned up, they submerged and followed her.
"I don't speak whale and I don't speak dolphin, but there was obviously something that went on, because the two whales changed from being quite distressed to following the dolphin willingly and directly along the beach and straight out to sea."
Another rescuer, Juanita Symes, added: "Moko came flying through the water and pushed in between us and the whales. She got them to head toward the hill, where the channel is. It was an amazing experience. The best day of my life."
Anton van Helden, a marine mammals expert at New Zealand's national museum, Te Papa Tongarewa, said the reports of Moko's rescue, while "fantastic", were believable because the dolphins have "a great capacity for altruistic activities".
He cited evidence of dolphins protecting people lost at sea, and their playfulness with other animals.
"We've seen bottlenose dolphins getting lifted up on the noses of humpback whales and flicked out of the water just for fun," he said.
"But it's the first time I've heard of an inter-species refloating technique. I think that's wonderful."
Since the rescue, Mr Smith said, the whales had not been spotted, although Moko soon returned to the beach and joined in games with local residents.
"I shouldn't do this, I know we are meant to remain scientific," he added, "but I actually went into the water with the dolphin and gave it a pat afterwards, because she really did save the day."
HISTORY OF SAVING LIVES
SINCE the mariners of ancient Greece regarded their presence as a good omen, dolphins have long enjoyed a reputation among fishermen and sailors for coming to their aid.
Roman mosaics and coins show images of men playing with dolphins, while in the 18th century, the Vietnamese navy was assisted by a pod of dolphins who helped rescue sailors whose boat was sunk by Chinese invaders.
In 2004, a group of swimmers who found themselves confronted by a great white shark off the coast of New Zealand claimed they survived thanks only to a pod of dolphins.
The huge shark came within two metres of the four swimmers, all of whom were lifeguards, but the dolphins circled them in a tight formation for around 40 minutes until the group were out of danger. Only when the dolphins were sure that the shark had disappeared did they open out the tight circle and allow the lifeguards to swim back to shore.
In 1996, meanwhile, a swimmer in the Red Sea was attacked by a mako shark, but may have survived thanks to a small pod of dolphins.
The attack occurred minutes after his friends – who had been swimming with the dolphins – boarded their boat, leaving the man alone in the water. A rescue vessel was sent to help him after the alert was raised, and found the dolphins were flanking the badly injured man.