There actually are/ were 13 artists using the Leviathan moniker (mostly rock/ metal apart from the act on the player with Thief Acrobat, which is lo-fi underground rap) :
1) Leviathan, aka Wrest, is a one-man black metal project from San Francisco, California. The band was brought to life in 1998 and has now been put to rest as of Oct. 2007. Wrest plays every instrument found in Leviathan's music: guitar, drums (electronic + acoustic), bass, synths, ebow, and vocals.
Leviathan has 15 demos from between 1998 and 2002.
Some of these, as documented by Maelstrom webzine are:
Shadow of No Light
Misanthropic Necro Blasphemy
Seven + Slaveship
Inclement Derision (Nine)
Sacrifice Love at Altar of War
Howl Mockery at the Cross
White Devil, Black Metal
Two full length albums have been released:
2003 - The Tenth Sub-Level of Suicide
2004 - The Tentacles of Whorror
There have been two CDs which compiled tracks from some of many of his demos which could be mistaken as full length albums:
2005 - Howl Mockery at the Cross
2002/2006 (recently re-pressed) - Verrater (a 2xCD)
Released in a strict amount of 500 and on vinyl only, was the 'A Silhouette In Splinters' album which, in the big scheme of things, was a compilation of intro's/ outro's and more ambient works from previous demos with renamed song titles (some Lurker of Chalice tracks are in effect, the same).
Recently, in another strict amount of 500 and on vinyl only, was the 'The Speed of Darkness' mini-LP which is just all his tracks from the CD split with Iuvenes released by No Colours in 2003.