"Kalag" is a title that has been used by many guildleaders of the Thieves' Guild in the Zoluren province since the original founding of the Zoluren's Thieves' Guild by Kalag Ka'Hurst, around the start of the Elanthian Calendar (Year 0).
These days, when people refer to "Kalag," they typically mean the Gor'Tog, Kalag The Black, who led the Thieves' Guild in the Zoluren area for most of the current era. Kalag the Black met his demise in Year 388 (October, 2007).
Varsyth, the current leader of the Zoluren guild, initially declined to take the name but on 26 Shorka 393 (February 4, 2009), he began to call himself Kalag the Sly.
See the founding guildleader, Kalag Ka'Hurst.
See the previous guildleader, Kalag The Black.