The Soda Poppers are triplets, though Peepers is one year younger than the others, due to a "very prolonged labor". They starred in the TV show of the same name, which began in either 1970 or 1971. However, their ages were given as 35 and 34 in Abe Lincoln Must Die!, which was released in 2007, an apparent contradiction.
In their first appearance, they had been hypnotised by Brady Culture, the former star of the show that the Soda Poppers replaced, as part of his plan to hypnotise the world into loving him. They were quite adept in the role as his minions, as their life-long addiction to Soda pop had imbued all three of them with super speed, requiring Sam & Max to employ great cunning in order to defeat opponents they couldn't catch. After Sam and Max stopped Brady Culture and cured the Soda Poppers' hypnotism, the Soda Poppers were left to beat Brady for his actions in hypnotising the three of them, whilst the Freelance Police left them to it.
It was ultimately revealed in the end of Season 2 that the trio had beaten Brady to death offscreen and subsequently had "realized that [they] were destined for much greater evil" than being child stars.
They next appeared on Embarrassing Idol, and developed a grudge against Sam and Max after they inconvenienced all three of them in different ways.
They then ran for governor of North and South Dakota, and, when all three were elected, split the two states into three, leaving Whizzer the governor of West Dakota. They later declared war on one other over who got Mount Rushmore.
At some point, they annexed Nebraska, and were all voted out of office. It was probably around then that they started their takeover of Hell, sending the Shambling Corporate Presence to Satan to make Hell more efficient. It was also around then that Sam and Max, who had previously treated the Soda Poppers similarly to most other characters, began to actively dislike them, probably as a result of fan hatred towards the child stars.
Each of the schemes to make Hell more efficient were stopped by Sam and Max, which turned to be exactly what the Soda Poppers wanted them to do, giving them an excuse to fire Satan and bring about Armageddon. However, Sam and Max also stopped them from doing that, and eventually trapped them on a small platform surrounded by lava. As they were swearing revenge and claiming that they'd be back, a Bermuda Triangle opened above them and covered them in lava, seemingly killing them. The Soda Poppers made no appearance in The Devil's Playhouse. ("Thank god").
In Beyond the Alley of the Dolls, when Sam and Max learned that the person who ordered the Sam clones had a very bright voice, Max, horrified, suggested that the Soda Poppers may have been responsible. It later turned out to be someone else. In The City that Dares Not Sleep, Momma Bosco used a low-frequency loop of Peepers' catchphrase "I can see you!" to keep everyone at BoscoTech awake.
Seeing as they were the princes of Hell, it may not be the end of the Soda Poppers yet.
Specs is a little bastard who gets annoyed when people ruin his graffiti, prompting him to say his tagline: "You made me mess up!". As seen in What's New Beelzebub, he is quite a demon. His demon form is the only one that is different from those of his siblings. He seems to think he's smarter than the other two and can be slightly condescending.
Peepers is named for his big eyes, which he occasionally draws attention to with his tagline: "I can see you". In What's new, Beelzebub?, Peepers tricks Sybil into being attracted to him, but she snaps out of it when it turns out that he was using a disguise when Sam reveal his real name to be "Dick Peacock."
Whizzer is named for his frequent bathroom breaks, which he often announces with his tagline: "Time out for number one!". Prior to Abe Lincoln Must Die! he swore off soda in order to get around this issue, but thanks to Sam & Max this change was a short-lived one. Whizzer's demon form looks identical to that of Peepers. In his demon form, he is able to pee fire.
Doug Boyd (Specs)
Peter Barto (Peepers)
Michael Barrett (Whizzer)