Joker (Shutnik / Шутник) is a stalker who appeared only in S.T.A.L.K.E.R.: Call of Pripyat.
An experienced stalker with a knack for telling jokes, Joker traveled the Zone together with Barge and Cardan. After a heated drunken argument, the group parted ways. Joker died sometime later in the Oakpine anomaly while attempting to obtain a Kolobok artifact from the anomaly's uppermost branches. His equipment and body decomposed due to the corrosive effect of the anomaly - only his PDA and partially upgraded (Psi +10%; Chem. +10%) Gas mask survived.
Call of Pripyat
Joker's remains can be found to the south of the Oakpine anomaly. They are bones with a gas mask and PDA nearby, so care must be taken when searching for them - they are easy to miss. The bright display of the PDA is a handy clue. Lowering grass draw distance can also help.