(Guildmaster) Darren Lightfinger is the founder and man in charge of the Thieves' Guild, found in the cellar underneath a house just north of the furnace in Lumbridge. Speaking to him begins the Buyers and Cellars quest. Depending on the amount of capers done, Darren's clothing improves.
Although Darren is thought to be a master thief, he will be amazed with the player's thieving abilities, if it is high enough, and asks them to teach him (requires level 61 or higher Thieving). Accepting this request earns 2,000 Thieving experience. Despite Darren's thieving abilities being lesser than the player's, he compensates with a variety of fences and contacts which allows him to make transactions wildly beyond the player's expectations as seen with the Capers.
The quote "It's the eye of the kyatt, it's the will of the heist... Again!" is a reference to the 'Survivor' song, 'Eye of the Tiger'.
The quote "Handkerchief on, handkerchief off" is a reference to the 1960 play "Oliver", based around the Charles Dicken's novel Oliver Twist. This connection is further reinforced with his next line "Oom-Pah-Pah - whoops that's not until the second act!" (Oom-Pah-Pah is another song from the play).
The quote "Handkerchief on, handkerchief off" may also be a reference to "Karate Kid" in which one of the training exercises consists of him waxing cars with the instruction "Wax on, wax off!".
If a player's Thieving level is high enough, attempting to pickpocket (through conversation options, not directly) the dummy will result in a humorous situation where the player stands next to the dummy motionless before performing the yawn emote. Darren will thereafter prompt the player to begin pickpocketing, only for the player to mention that he/she has stolen the handkerchief. The player would then begin teaching Darren the same tricks as he taught the player before, by pickpocketing the dummy several times. He would then make a humorous comment on how he couldn't have put it anywhere near as good, despite the player directly quoting what he had taught before. The player would then gain a one-time reward of 2,000 Thieving experience.