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)
Ten
Sacrifice Love at Altar of War
Intolerance (Eleven)
Howl Mockery at the Cross
White Devil, Black Metal
Fifteen


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.

Another LP released in late 2006 was 'The Blind Wound', this too was material previously released from one of many split CDs. This however, was pressed in an edition of about 2000 copies.

Leviathan also covered 'My War' by Black Flag for a Thrasher (skate board mag) compilation. The track can also be found on the latest Southern Lord Records sampler CD.

Beyond doing Leviathan, Wrest has a 'side project' under the name of Lurker of Chalice which blends the lines of black metal and neo-folk with a dark ambience.

Wrest has also performed with Sunn O))) and Twilight as well as playing drums for Nachtmystium for some live appearances.

Also noteworthy is his prior band called Gift Horse, a Cali based instrumental rock band in which he played drums for.

Wrest's real name is Jef Whitehead (one F, please reference Black Heart Tattoo's web/myspace page for correct spelling), and outside music he is a famous tattoo artist and artist (created the cover art for the recent Cult of Daath 2xLP (released by NWP!) and works with Hildolf aka Tim Lehi, who is Draugar, at Black Heart Tattoo.

As of Oct. 24, 2007, Blake from Nachtmystium and owner of Battle Kommand Records has posted the following about demise of Leviathan:
"This is now a Nachtmystium / Lurker of Chalice split as Wrest has completely killed off Leviathan and will be working primarily under the LoC moniker from now on. nothing else to say about that..."

The post he created about the situation can be viewed here.

2) Leviathan is an underground rapper from Minneapolis signed to Insides Music. In 2006 he released his first album Thief Acrobat and Armed Response. His style is spoken word poetry over mellow, lo-fi backing, similar in sound to The Last Poets or Gil Scott-Heron, crossed with the wordplay of modern artists such as The Gift Of Gab but with a more laidback flow than all of these.

3) Leviathan is a dark ambient project from UK under Monkeyhouse Records. Albums: The Throne of Bones (2002), Machinery of Hell (2003), Shrouded By Fog (2003). Now known as LVTHN.

4) Leviathan from NY, Thash Metal band USA had Chris Barnes from Cannibal Corpse and Six Feet Under in it

5) Leviathan ??, USA, had a track on 'Metal Dreams' compilation

6) Leviathan from Colorado, USA who released three full length albums

7) Leviathan from Turkey, released the album 'Cold Caress'

8) Leviathan from Sweden is a black metal band who released the album 'Far Beyond the Light'

9) Leviathan from Germany, released two demos and had a member from Necrophagist

10) Leviathan from Spain who had members in Innerself

11) Leviathan from Argentina who released three full length albums

12) Michel Klaasen, known as Tellurian and Leviathan, is the man behind the Cenobite label. The music on this label is a mix between underground Trance and hardcore: Trancecore! Lately he also has a live act together with the Predator.

13) Leviathan from Italy, a progressive rock band who, in 1988 and 1990, released two neo-prog albums in the English language before a lengthy hiatus. In 1998, the band returned with an Italian language album of a similar musical style. Another album in Italian followed in 2004.