I'm not sure who to credit for the following story because it has been used on numerous sites, but I would like to thank whoever it was who wrote it because it is the most thorough yet condensed description/history I (and apparently many others) have ever read. Perhaps I will make an attempt in the near future to shorten it just a little more once the page is all up and running.
I'm adding the continuation of the story as well as anything I feel should be included to give fans a better understanding of the boys as I go along. Keep in mind the best way to look into the Dassings' minds and lives is to read the numerous interviews available; we've compiled a bunch for you in the links section.

"Mentallo and the Fixer is the industrial brainchild of two brothers from Texas, Gary and Dwayne Dassing. Mentallo and the Fixer derived its name from a pair of comic book characters whose origins have long since faded into obscurity.The Dassing brothers were raised on rock music, so their first instruments were actually the guitar (Dwayne) and drums (Gary). However, this changed when the pair discovered a number of new wave bands whose music was heavily saturated with synthesizers. Dwayne specifically lists the Cars, early Orchestral Manouevres in the Dark, and especially Gary Numan as storng influences to Mentallo and the Fixer.
Around 1984, the brothers began acquiring synthesizers, discovering the inherent sonic possibilities that these instruments allowed. They began to experiment with these instruments, with recording techniques, and even rudimentary sampling with taped based equipment.
In 1988, the brothers added vocalist Rich Mendez to their roster, and adopted the name Benestrophe. They made two tapes as Benestrophe using only a 12-channel mixer and a $100 stereo TEAC tape deck (incidentally the same equipment used for the first Mentallo release), and surprised even themselves with its sound quality. Much of these tapes are now available on Benestrophe's Sensory Deprivation CD and Auric Fires (RAS DVA).
Benestrophe ended in 1990 when the Dassings moved to another part of the state, and then began their work as Mentallo and the Fixer. A DAT tape of No Rest for the Wicked was sent to Portugal's Simbiose Records, and was released on vinyl in a limited edition of 500. (It was re-issued on CD by Metropolis in 1998 as a double CD with additional unreleased tracks and remixes.) A subsequent tape was sent to Talla 2XLC of Zoth Ommog fame, who signed the band to a three-record deal within two weeks.
Though actually their second album, Revelations 23 was their first proper release, and gained the attention of Metropolis Records, who began their long association with Mentallo and the Fixer with this release. Like its predecessor, Revelations 23 was filled with anger: snarling distorted vocals, hard cutting sequencer rhythms, and a thunderous beat.
Their next CD, Where Angels Fear to Tread, displayed considerably less rage than their previous work. The CD showed tremendous musical growth and artistic maturity, being very complex and emotional, with dark Gothic overtones. The CD was met with almost universal acclaim.
In 1994, the Dassings joined forces with vocalist Michael Greene to create the trio Mainesthai, releasing Out to Lunch and Mentallo Meets Mainesthai, which was more melodic and humanistic than Mentallo. Both were released on Metropolis in 1998.
In 1995, Mentallo and the Fixer signed exclusively with Metropolis Records, and began doing remixes for other artists, including one for Haujobb. 1996 saw Mentallo's first national tour, which was met with rave reviews by both critics and audiences alike.
Following this tour, Mentallo and the Fixer began on their next album Burnt Beyond Recognition, which was released in 1997. In addition to the album, Gary and Dwayne put together two singles for Burnt Beyond Recognition, called Centuries and False Prophets.

1999 saw the departure of Dwayne from Mentallo and the Fixer. Gary continued on his own, with the release of the Systematik Ruin single and the Algorythum full length CD. Gary's vision is different from his previous work, with the incorporation of live drumming, a more experimental approach to electronics, and a more positive outlook on the state of things.
Gary returned in 2000 with a final Mentallo and the Fixer album, called Love is the Law, which is aimed especially at all of the underground fans who have supported his work.
New for 2001, Grimpen Ward features fourteen freshly re-mixed tracks that span over Mentallo and the Fixer's ten year career. Classic tracks like Legion of Lepers and False Prophets have been fused with new styles and ideas to add an entirely new dimension of artistic creativity. This release takes old favorites with the latest sounds to create a 'best of' unlike no other. This led to a stir of emotions and a spark of creativity.
Now, the brothers are back! Just when the world thought they saw the end of Mentallo & the Fixer, the dastardly duo return with Vengeance is Mine. Gary and Dwayne Dassing stir up a concoction of pounding beats, and sticky electro synths that will cling to your soul to get you moving."

Gary has currently been focusing on his latest project, Shimri, and has already released his first cd entitled Lilies of the Field on Art Of Fact Records. Dwayne is also composing music, but has not released anything as of yet, although Gary has previewed some songs and has liked what he heard.