Alicarus Vorasik was born to an elven couple in Korvosa. He grew up relatively happily for a time, displaying some small talent for future magic or some such, and was kept safe from the harm and danger of the city streets. But when he was separated from his parents on the street--while he was watching a street magician ply his trade, the elves were accosted by Hellknights--it was the local thieves who found the elven child wandering in tears. They took him in and taught him
their way, and he spent most of his many formative years in the markets of Korvosa, learning what was worth taking and who wouldn't catch you. He eventually graduated from a distraction to the pickpocket, and from there to a full-fledged thief. He learned how to hide knives on your body, as well as other items. He even picked up the trick of activating magical devices that would only speak to mages--unless you had the right knack.
From Korvosa Alicarus jumped onto a Sczarni caravan, and rode with them for a while. He worked his "magic" and duped fools out of their gold, and learned that a silver tongue and a sharp mind can be infinitely more powerful than quick hands and a hidden knife--though all four are certainly good to have.
When the Sczarni found themselves in Magnimar after a few years' travel, Alicarus hopped off there, met up with the city's thieves' guild, and joined with them. Again, he spent several years practicing his work here, but his ambitions were growing. Alicarus soon discovered he didn't want to be just a cronie, a henchman; he wanted to become a crime lord himself, the leader of a gang of thieves more renowned than any Golarion had yet seen.
So Alicarus met up with another caravan and headed north to the frontier town of Sandpoint, where he hoped to forge his own legacy among the thieves of the world, under the guise of "The Mantis"--certainly a fear-inducing name.