In order to obtain the Founding Titan, Marley commenced the Paradis Island Operation, deploying a total of 3 Warriors, each with a specific role.
Annie, the Female Titan, transported the team to Wall Maria, while luring and gathering Pure Titans.
Bertolt, the Colossus Titan broke the outer wall, while Reiner, the Armored Titan breached in inner walls, spilling the Titans into Shiganshina.
This allowed them to infiltrate Paradis to attempt to steal the Founding Titan.

Correction

Um actually … Marley deployed 4 Warriors. There is also Marcel, who was supposed to transport the team together with Annie, but he was eaten by a Titan in Paradis.