First Appearance: Joker: Last Laugh #1 (Dec. 2001): "Stir Crazy"
Number of Appearances: 1
Enemy of: The Joker
Employer: Slabside Island Maximum Security Prison
Note: guard at the Slab (super-villain prison)
The guard named Clarkson worked at the Slabside Island Maximum Security Prison. Clarkson is mentioned in panel 1 on page 6 in Joker: Last Laugh #1 (Dec. 2001). (This is on page 10 in the Joker: Last Laugh trade paperback.) In this panel Black Canary is viewing Oracle's computer screens, which are showing footage of a prison riot at the Slab. In the bottom-center screen, we see one guard speaking to Clarkson (who is not on screen). The guard says, "Clarkson! We need a sit-rep from your position!" The word "sit-rep" is short for "situation report."
Clarkson is never shown in this comic. Or, if he is shown, he is unidentified. There are many unnamed prison guards in the story. Essentially all of the guards were murdered by the rioting and escaping prisoners during the this and the following issue of the Joker: Last Laugh mini-series. Whoever Clarkson was, he was almost certainly among the murdered guards.