Dex was one of the people affected by gang violence spreading throughout Stilwater and thus joined the gang formed by Julius Little, the 3rd Street Saints, to rid the city of its chaotic state. Dex appeared to be the voice of reason amongst Little's lieutenants. Dex is a superb tactician, but talk amongst the generic Saints gang members that wander the streets seemed to indicate that few Saints believe that Dex deserved his post and there was concern that Dex might have eventually challenged Julius Little for control of the gang. Dex seems to have a reasonably balanced attitude towards violence. 
Talk amongst the generic Saints gang members also indicates that Dex has a fondness for prostitutes and also has a younger sister. Dex is unquestionably the brains of the Saints organization as his credits include framing of the Vice Kings in an effort to draw public attention to the Vice Kings, as well as drafting the plans that lead to the assassinations of Los Carnales jefe, Hector Lopez, and Stilwater police chief, Police Chief Monroe.
Before The Protagonist was blown up on Alderman Richard Hughes' boat, Dex dropped his flags after he was offered a job in Ultor by Dane Vogel at the Saints' church. He called Troy Bradshaw after this happened, telling him that he knew Troy was a cop and he was out of the Saints, and wanted to make sure he and Troy won't have a problem (due to Troy being able to arrest him).
During the time that the Saints and Ultor were at war, The Protagonist visited the police station and listened to the conversations that were taped. He found out that it was Julius who put the bomb on Alderman's boat. He also found Dex's file containing his phone number. The Protagonist called Dex and he told him to come meet him at the church so that they could get rid of Julius. However, this was a trap set up by Dex and instead of Dex, Julius showed up and after a conflict between Julius and The Protagonist, a smoke bomb was thrown through the church's window. Dex had sent a Masako to get rid of the two, but they failed.
Some time after, Eric Gryphon, Ultor's new CEO, visited the Saints telling them that he wanted protection from the Masako who were sent by Dex to kill Gryphon. The Protagonist successfully protected Gryphon from Dex's assassination attempt. After this Gryphon and Dex met in front of the Phillips Building and talked about Dex's attempt.
Then Gryphon informed The Protagonist that Dex was selling toxic waste to illegal buyers. The Protagonist, with help from Ultor security, succeeded in stopping Dex's plan. Dex felt the heat closing in on him and asked for an immediate transfer to another Ultor branch.
Gryphon again informed The Protagonist that Dex fled and that he couldn't do anything. However, The Protagonist still wanted to hurt Dex hard and Gryphon came up with a plan. While Gryphon was standing on the lighthouse informing The Protagonist of any of Dex's acquaintances walking around, The Protagonist killed them. After this happened, The Protagonist said he would find out which city Dex ran to and to get him.
Dex's pet peeve is people using the wrong terminology. Dex often states "It's 'The Carnales' or 'Los Carnales', not 'The Los Carnales'".
Dex and Julius are the only Saints that are not unlockable homies in any of the games, and The Protagonist has a deep hatred for both of them in Saints Row 2.
Dex's hair, grammar, clothing style, and even voice, have changed dramatically from Saints Row to Saints Row 2. This suggests that he was very young in the first game, a teenager.
Dex's phone number in Saints Row 2 is 555-2628, but the number will not work unless his number is already in your Phone Book.
Dex sometimes appears again in your phone after completing the Revelation mission, and if you call him you can sometimes unlock the mission again and play it without using the Newspaper Clipboard.
As of Saints Row: The Third, Dex and Troy are the earliest known members of the 3rd Street Saints who have not been killed.
In a livestream interview with Destructoid one week prior to the release of Saints Row: The Third, Steve Jaros, one of the writers of the Saints Row series, confirmed that Dex does not appear in Saints Row: The Third. Jaros further explained that Dex was to appear in another project which "never materialized", and Volition, Inc. did not want to put Dex in the game and alienate players who did not play Saints Row or the Saints Row 2 DLC Corporate Warfare.
Dex was to feature in a spin-off titled Saints Row: Money Shot, where he was to be shot and killed by an assassin working for Ultor, in a mission titled "Dex's New Digs" .