Originally a scientist who worked in the same lab as Dr. Crabtree, Dr. Schlock first appeared as a walk-on character administering cosmetic tests on Bun-bun, where it appears he lost his left eye and now has to wear an eye patch (confirmed in Broken chapter when he faces Frog without his eyeglasses [http:// "Sluggy Freelance: 3/20/2009".] ) .
He later appeared as an old man from the future of an alternate timeline where K'Z'K had taken over the world. His knowledge helped save the current timeline from that same fate. Not truly a villain, only incredibly selfish and cowardly, making Schlock an anti-hero of all sorts. He would occasionally aid the main characters with insider information (having been involved with Hereti Corp entirely against his will) or inflatable technology from the future, but only when threatened with significant bodily harm. Indeed, a recurring gag in the webcomic is that, every time Schlock thinks he's safe from his enemies, Riff appears out of nowhere with a ray gun pointed into his ear (in the "book" Aylee, a disgusted Schlock asks how he(Riff) does that). However, he's a slippery and clever opponent, having gained the better of both Dr. Crabtree and Hereti-Corp by cunning when they were after him. Due to his attempts at cloning Aylee, he knows more about her physiology than anyone else alive. Because the currently active timeline diverged from the one which the old future version of the doctor came from when K'Z'K didn't conquer the world, this Schlock has remained unaffected by the death of his "present-day" self at the hands (and fangs) of Dr. Crabtree and has long been the only one remaining.
Recently, Schlock was seen living with Torg and Riff, helping them keep Aylee alive, and Riff was helping him with his 'evil' issues. After to constant encounters with a naked Gwynn, he gained a severe crush on her  which appears to have ended after she kicked him immensely hard in the privates. When Aylee's latest form emerged, Schlock tried to escape (with Riff's Dimensional Flux Agitator in tow) without being detected, but ended up chased by both Hereti-Corp and the government. He evaded both for a time, but offered to make a deal with Hereti-Corp by offering them a functional Dimensional Flux Agitator, in turn receiving a share of the company's stock and the position of the head of R&D. However, he had been secretly buying Hereti-Corp stock through a number of shell companies, and managed to acquire a controlling interest in the company, proceeding to make himself CEO and fire Daedalus. Later, he used Kusari to get rid of the government agents tracking him by killing them. Though expressing reluctance to having taken such an evil path in the first place, he now intends to continue Hereti-Corp's plans for world domination.
Update: he failed.
Dr. Irvin Schlock is a man who reappears in many different dimensions and timelines, being a timeline traveler in the main Sluggy dimension.
In the Ghoul Dimension, Schlock was already dead when Torg arrived, having made many technological advances to benefit the surviving human population.
Schlock have an alternative in the Dimension of Rain, but his condition and story is a major spoiler...
This section blatantly gives away the mysteries and/or endings of the storylines 4U City Red.
If you haven't read some of those stories, then dude, before you go any further, go read them! This stuff will still be here when you're done.
You have been warned...
In the Dimension of Rain, Schlock is revealed to play a major role for the entire dimension. He prevented the rise of K'Z'K, ended the R&D Wars, and was His Masterness until his death. Like the main dimension Schlock, he betrayed that dimensions Riff (DoR) and Zoë (DoR), due to Riff "having a knack of finding out his hiding places". Schlock was also the father of Executive Rammer.