Character Analysis
Marquez is a stoolie—he's got dirt on Keyser Söze's true identity, and he's willing to tell it. Argentinean gangsters are selling Marquez to Söze's rivals, a Hungarian gang, who will try to use the info he gives them to bring Söze down.
But, Marquez has bad luck—Keaton and Co. kill most of the Argentinean and Hungarian gangsters on the dock, leaving room for Söze to sweep in and kill Marquez. This teaches the viewer a valuable moral lesson: snitches get stitches (unless they're snitching to the police—that's a probably good thing; just don't snitch to Hungarian gangsters).