ORIGINAL: WS
When the wings are staggered, the forward wing will stall first. In this case, the top wing is set negative to the bottom wing to make them stall evenly (more aggressive). Having the forward wing stall first makes for more gentle stalls, since loss of lift ahead of the CG will naturally cause the nose to drop when it stalls, while the bottom wing still flies.
Right...On negative stagger biplanes like the Beech Staggerwing, Beercat, Stitts Skybaby, etc., the lower wing is set to stall first.