A ninja (“one who is invisible”) or shinobi (“one who sneaks”) was a covert agent, mercenary, or guerrilla warfare expert, in feudal Japan. The functions of a ninja included siege and infiltration, ambush, espionage, deception, reconnaissance and body guarding. They had great fighting skills in martial arts, were experts in disguise and used a large variety of tools and weaponry. Ninja became mostly known as specially trained warriors, spies, and mercenaries during the Sengoku period (15th-c.). Following the unification of Japan under the Tokugawa shogunate  (17th-c.), the ninja faded into obscurity. Soon, they had become a topic of imagination and mystery. Ninja figured prominently in legends and folklore, where they were associated with legendary abilities such as magical means of camouflage, walking on water, invisibility and control over natural elements.