Sphinx

Sphinxes are magical creatures issued from ancient Egypt and Greece mythology. In the series American Dragon: Jake Long, they are the source of a major weakness to Dragons. Because they are only mentioned and never seen in the series, their true form currently remains unknown.

Physical Appearance
Although Sphinxes are never seen, it is possible they take either one of two forms.

Egyptian
In Egypt, Sphinxes are usually depicted as having a lion's body and the head of a human. Their face is usually male, but representations of female figures have also occurred. Sphinxes can also have the head of a ram. They were often considered benevolent and placed at the doors of temples.

Greek
In Greece, Sphinxes also have the body of a lion and a human's face. However, the head is exclusively female, in contrast to the Egyptian Sphinx. In most depictions, they also have a giant pair of wings. In ancient Greece, they were considered treacherous and merciless.

Powers and Abilities
From what was shown in the series, Sphinxes are powerful creatures that Dragons avoid at all cost. The reason for this is that a Sphinx' hair has a draining power that can absorb a Dragon's strength until it reaches a weakened and powerless state. Often, Dragons will become so weak that they will revert to their human selves. If exposed long enough, they will also be unable to walk properly and may even be knocked out completely.

Strands of Sphinx hair are often used to create Dragon slaying gear, mostly full-proof nets. These nets can also affect other magical creatures, such as Yetis and Griffins (as seen in "Ski Trip" and "The Egg" respectively), although they do not appear to sap these creatures' energy. Other Dragon slaying products made out of Sphinx hair include strengthened chains and spears.

Most magical creatures know about the Sphinx' effects on Dragons and will not hesitate to use this to their advantage.

Life in the Magical World
Because not a single Sphinx has been shown in the series, it is possible that they remain mostly in their respective land (Egypt or Greece) and rarely head out to other territories. Another explanation would be that, if following the theory of them being very dangerous creatures, Sphinxes are kept in captivity as to keep them from going on a rampage.

The possibility of the Sphinx being extinct is impossible since their hair is constantly being used for various hunting gear.

Trivia

 * In Greek mythology, the Sphinx is known to give riddles to travelers, the most famous being: "What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?" (the answer is man);
 * In the episode "Fu and Tell" (Season 1), it is revealed that Fu Dog and Yan Yan accidentally broke the Great Sphinx of Giza's nose during one of their quarrels;
 * In the Strigoi native tongue, a spear on which is attached a braid of Sphinx hair is called a "tarizman kill Dragon nosa" (which roughly translates to "Dragon slaying talisman").