Telekhine

"After we made so many of the gods' finest weapons. The trident of Poseidon, for one. And of course - we made the greatest weapon of the Titans! Nevertheless, Zeus cast us away and relied on those fumbling Cyclopes. That is why we are taking over the forges of the usurper Hephaestus. And soon we will control the undersea furnaces, our ancestral home!"

- The Telekhines' plan

Telekhines (also known as Telchines or Telkhines) are mysterious smiths and sea demons native to the islands of Keos and Rhodes. They are the children of Thalassa and Pontus.

History
They invented the art of metal-working and were said to have crafted the scythe Kronos used to castrate his father Ouranos and later a Magical Trident for Poseidon which the god used to level mountains into the sea and form the islands. Their malignant use of magic, particularly, they produced a mixture of River Styx water and sulfur, which killed plants and animals, angered Zeus, who cast them beneath the sea or into the very depths of Tartarus. Telkhines were sometimes described as having the head of a dog and fish-flippers for hands. They're also known as "fish children."

The Battle of the Labyrinth
They made weapons for the Titans and used Hephaestus' forge, under Mount Saint Helens. Percy Jackson spied on them and burst out while the younger Telekhines were watching a documentary. It is learned that they are on the side of Kronos, holding a grudge against Zeus and the other Olympian gods. They had to leave the forge when Percy caused the volcano to blow and he almost dies. But he goes to Calypso's island - Ogygia. Later some Telekhines were seen with Ethan, carrying Kronos' scythe, helping to resurrect the Titan on Mount Tamalpais.

The Last Olympian
When Percy was aboard the Princess Andromeda with Beckendorf, he spared a telekhine, partly because his "Li'l Demon's Lunch box" was cool and partly because he needed it to sound the alarm. The East River Spirit reminded Percy of a telekhine. They were also seen fighting among Kronos' troops in the Battle of Manhattan.

The Mark of Athena
Telekhines are seen in a tank at the Georgia Aquarium building things out of LEGO. Phorcys gives them a cue to leap in their tank, do a synchronized double flip and land in pyramid formation but is ignored by the sea demons.

Appearance
Telekhines have faces like dogs, with black snouts, brown eyes, and pointy ears. Their bodies are sleek and black like seals. They have stubby legs that are half flipper and half foot, and human-like hands with sharp claws. Percy described that if you blended together a Doberman pinscher, a human child and a sea lion, they'll look like a Telekhine. Fully grown adult telekhines can be up to seven feet tall. Telekhines bark and growl, and they waddle instead of walking.