Mojo is the essence of Austin Powers' sex drive. It was what gives him his legendary sexual prowess and his potency. Physically, it is a fluid inside Austin's testicles that is the source of his potency and his amazing sexual prowess.
Stolen
In the movie, The Spy Who Shagged Me, Austin's mojo was stolen by Fat Bastard in the year 1969 as Austin was sleeping with Ivana Humpalot in 1999, rendering him impotent (erectile dysfunction). With his mojo gone, Austin went through an existential crisis, not only feeling less virile with his libido gone, but fearing he had also lost his skills to stop Dr. Evil. Also, despite his mutual desire to shag Felicity Shagwell, he had to turn down the young swinger's advances out of humiliation of being unable to please her sexually, although the two did make up once Austin admitted the truth about his impotency. After stopping Dr. Evil from destroying Washington D.C, Austin's nemesis intended to at least get some revenge by ensuring the spy remained impotent forever. Taking out the bottle with Austin's mojo, he threw it into the air, hoping to destroy it. Both Austin and his past self tried to save it, only to crash into each other before either could catch it. The bottle crashed to the ground, destroying Austin's mojo as Dr. Evil's base exploded around them. While Austin felt defeated, however, thanks to Felicity's encouragement, Austin realized he had his mojo inside him all along. Later in a post-credit scene, Austin's past self is seen shagging Felicity, to which present-day Austin realizes he has gotten his mojo back. With their mojo returned and thus their virility, both Austin's made their move on Felicity, ready to have a threesome.