Dennis R. Reynolds is the co-owner of Paddy's Pub, and Dee Reynolds' fraternal twin brother. Dennis is best friends with Charlie and Mac, the latter being his roommate.
Dennis is portrayed by Glenn Howerton.
- Dennis is highly narcissistic and has delusions of grandeur.
- His grandiose delusions cause Dennis to believe that he is extremely attractive to others. He often "pops off" his shirt in inappropriate situations. He frequently obsesses over any possibility that he may have a visible physical flaw and often spends the remainder of the episode trying to correct it. Dennis is actually very insecure about his looks. Any critique of his looks, however mild or trivial, deeply distresses Dennis and often leads him to extreme behavior. When Dee countered Dennis' insults by claiming that he has a "fat face," it temporarily caused Dennis to become dangerously anorexic. ("The Gang Exploits A Miracle")
- Dennis' delusions of grandeur extend to his relationships with others. In high school and later in college, Dennis believed that he was a legend that others looked up. He later found out that he was wrong on both counts. ("The Gang Reignites the Rivalry") ("The High School Reunion, Part 2: The Gang's Revenge")
- Dennis demonstrates characteristics of psychopathy, and is almost wholly unable to empathize with others. He routinely destroys others' property, and casually mentions psychopathic acts without any awareness that others might be disturbed by them:
- Dennis vandalized Art Sloan's house, and set his yard on fire. ("The Gang Reignites the Rivalry")
- He offered to "frame bang" the Lawyer's wife, and was surprised when the Lawyer referred to it as rape. ("Paddy's Pub: Home of the Original Kitten Mittens")
- Dennis is obsessed with sex. He has had sex with many women, and has both audio and video recordings of his sexual encounters. He's also claimed that, in his sexual encounters, the words "no", "don't", and "stop" never stop him from following his intentions. ("The Aluminum Monster vs. Fatty Magoo") Members of The Gang comment on his attraction to teenage girls in "Underage Drinking: A National Concern"; in this episode, Dennis ends up being tricked by an eighteen-year-old high school senior into plowing her at her high school prom. Dennis also has a fascination with anonymous sex, even going so far as to install a glory hole in the men's room at Paddy's.
- Dennis is also implied to have had a gay experience while blackout drunk at the beginning of the first season when Mac, helping Sweet Dee get revenge, got Dennis drunk on tequila. Dennis shows a comprehensive understanding of the mechanics of gay relationships. He knows what it means to be a bear or a twink and understands how a "top" differs from a "bottom"; he explains to The Gang that "speed is the name of the game" when defining the role of a "power bottom". Frank also pimped out Dennis as a "no rules" prostitute in "The Gang Gets Whacked (Part 1)", telling clients that Dennis would "do anything with the ass." The ambiguous nature of Dennis' sexuality has been explored in other episodes and is usually connected to his vanity and need for peer approval.
- Dennis insults and demeans his friends on a regular basis, particularly Dee and Charlie, and never hesitates to draw attention to their flaws, shortcomings, and past failures.