Red and Black
Redaxe is an amorous dwarf (he stripped the Vestal Virgins of the property of "Virgins"), who is armed with an arquebus and has a penchant for explosives, while the other is a skilled Shadowdancer, who only after spending many years in his prestige class realized that the world of the stick figure comic lacked any shadows in the first place.
Due to a misunderstanding with the hotel staff reminiscent of the Who's on First? routine, Roy was treated as the King of the country of "Nowhere". The two assassins then attack him, poisoning Elan in the process and forcing Roy to use the Girdle of Feminity/Masculinity to get the bard to safety.
Once he escapes, Roy returns with Haley and Vaarsuvius to confront the assassins. In the chaos, a passing Belkar accidentally sets off one of Redaxe's barrels of explosives, destroying the inn with much of the Order's treasure and inducing Haley's aphasia. In the resulting explosion, the Shadowdancer finally finds a shadow he can teleport through, and the assassins escape.
The pair of assassins make an appearance where they are spying on Thanh's meeting with the real King of Nowhere. The two cancel their new attempt to assassinate the King, apparently basing this decision entirely on Thanh's presence. Presumably they either abandoned their plan or waited for Thanh to depart before their next attempt.
The pair of assassins also appear as monster cards in The Order of the Stick Adventure Game. "The Shadowdancer", as the game refers to him, remains anonymous, whereas the dwarf's card is titled: "Kaboom" Redaxe.