In folklore, a mermaid is an aquatic creature with the head and upper body of a female human and the tail of a fish. Mermaids appear in the folklore of many cultures worldwide, including the Near East, Europe, Asia, and Africa. The first stories appeared in ancient Assyria, in which the goddess Atargatis transformed herself into a mermaid out of shame for accidentally killing her human lover. Mermaids are sometimes associated with perilous events such as floods, storms, shipwrecks, and drownings. In other folk traditions (or sometimes within the same tradition), they can be benevolent or beneficent, bestowing boons or falling in love with humans.
Some of the attributes of mermaids may have been influenced by the Sirens of Greek mythology. Historical accounts of mermaids, such as those reported by Christopher Columbus during his exploration of the Caribbean, may have been inspired by manatees and similar aquatic mammals. While there is no evidence that mermaids exist outside folklore, reports of mermaid sightings continue to the present day, including 21st-century examples from Israel and Zimbabwe.
In Scottish mythology, Selkies or Selkie folk meaning "Seal Folk" are mythological beings capable of therianthropy, changing from seal to human form by shedding their skin. They are found in folktales and mythology originating from Orkney and Shetland. The folk-tales frequently revolve around female selkies being coerced into relationships with humans by someone stealing and hiding their sealskin, thus exhibiting the tale motif of the swan maiden type.
There are counterparts in Faroese and Icelandic folklore that speak of seal-women and seal-skin. In some instances the Irish mermaid (merrow) is regarded as a half-seal, half-human being.
The male equivalent of the mermaid is the merman, also a familiar figure in folklore and heraldry – legendary creatures who have the form of a male human from the waist up and are fish-like from the waist down, having scaly fish tails in place of legs. Although traditions about and sightings of mermen are less common than those of mermaids, they are generally assumed to co-exist with their female counterparts. A "merboy" is a young merman.
In contrast to mermaids, mermen were traditionally depicted as unattractive. However, some modern depictions show them as handsome.
In Greek mythology, mermen were often illustrated to have green seaweed-like hair, a beard, and a trident. In Irish mythology, mermen (merrow) are described as extremely ugly creatures with green hair, teeth and skin, narrow eyes and a red nose.
The actions and behavior of mermen can vary wildly depending on the source and time period of the stories. They have been said to sink ships by summoning great storms, but also said to be wise teachers, according to earlier mythology. Mermen, just like mermaids, can lure and attract humans with their enchantingly beautiful, soft melodic and seductive siren-like singing voices and tones.