As the name implies, Judge Cal was inspired by the real-life Emperor Caligula, whose stories of madness long outlived his reign. Whether they were true or not, certain elements such as Emperor Caligula appointing a horse as Consul has parallels with Judge Cal's appointment of his goldfish as Deputy Chief Judge. Judge Cal is also designed to give a patrician appearance, mimicking features of Roman and Greek marble statues such as his hair style. Judge Cal's all around madness and hallucinations share traits with both Emperor Caligula as well as Emperor Nero. Much of Judge Cal's eccentricities were played up for the full effect of absurdity and dark humor that the 2000 AD strip was beginning to be known for at the time.
The Day the Law Died
Head of SJS and rise to Chief Judge
Judge Cal was initially the head of SJS (Special Judicial Squad), which acted as an internal police for the Judges in Mega-City One. The position afforded him a lot of power, which he manipulated through blackmailing of judges caught in his investigations. As the head of SJS, Judge Cal had a position on the all powerful Council of Five, where all the major functions of the Justice Department, and by extension Mega-City One, were vested in. Judge Cal eventually ascended to the position of Deputy Chief Judge, and attempted to use his position to frame Judge Dredd in the murder of a journalist by way of a robot to weaken Judge Goodman, who trusted and defended Judge Dredd. Cal hoped that the ensuing embarrassment and shame from defending Judge Dredd after his conviction would prompt Goodman to step down; however Judge Dredd was able to prove his innocence once defeating the robot double, leaving Cal to find another way to remove Goodman.
Judge Cal's machinations eventually come to fruition when he orchestrates the assassination of Chief Judge Goodman and takes power due to his position as Deputy Chief Judge, promptly filling the position of Deputy Chief Judge with his goldfish. He quickly asserts himself and gains supporters, attempting to assassinate Judge Dredd who receives from the dying Goodman an SJS emblem he grabbed from his attackers, linking Judge Cal to the crime. Judge Dredd narrowly survives the assassination attempt and is taken to a hospital, where Judge Dredd is surprised by the support Judge Cal is able to receive from the Judges, which is later found out to be because of subliminal messages he inserted into the Judges' daily briefing videos to demand complete obedience to him weeks before Judge Cal made his move for the office. Judge Cal tries to have Judge Dredd executed after he is captured by his men, but Dredd escapes thanks to the help of his friend Judge Giant.
Judge Dredd then attempts to make a move to unseat Judge Cal by force with the backing of an angry citizen mob, but fails when Judge Cal calls upon his reinforcement of Klegg mercenaries to disperse Dredd and the citizens, driving Dredd and several judges underground.
Descent into Insanity
With Judge Dredd out of sight, Judge Cal goes about reshaping Mega-City One in his insane image. One of his first acts is to re-instate the death penalty, which had up to that point not used by the Justice Department. Judge Cal in his moment of insanity then decides to implement mass executions as punishment for the citizen mob supporting Judge Dredd, which is only narrowly averted when Judge Fish is "assassinated" by one of his aides, Judge Slocum, on the request of Dredd to prevent the mass executions. Judge Cal arranges for a funeral and a day of mourning for his dear pet, but is further enraged when, surprisingly, no one shows up for the funeral procession. After appointing the leader of the Klegg mercenaries, Grampus, as the new Deputy Chief Judge, Judge Cal proceeds to implement a whole range of oppressive laws right down to minor acts, almost all of which were punishable by death. This prompts many citizens to try and leave the city.
In order to prevent the exodus of Mega-City One citizens from the city, Judge Cal then employs the use of forced labor to build a massive wall separating the city from the Cursed Earth, effectively imprisoning all of Mega-City One. With his brainwashed Judges supplemented by his Klegg mercenaries, Judge Cal's rule seems to be unstoppable. Judge Dredd re-emerges once again to attack the teams constructing the wall, prompting Judge Cal to direct a massive operation to flush him out. Judge Cal leaves Dredd for dead when he and his allies plunge into the underground of Judge Dredd near the "Big Stinky", the former Ohio River.
Judge Cal, aware of Judge Dredd's appeal among the masses, arranges to have a dramatic movie produced about his life, airing a famous Mega-City One actor to play himself while having a midget play Judge Dredd, glorifying his exploits and demonizing Judge Dredd. When Dredd once again shows that he has not died, Judge Cal enters into a moment of rage and nearly destroys Judge Dredd's servant, Walter the Wobot. Walter however plays to Judge Cal's desires, claiming he does not like Judge Dredd and giving him a great deal of false information on Dredd. Cal then appoints Walter as the first robot Judge, and uses his statements in a campaign to discredit Judge Dredd. Judge Cal "pickles" Slocum in a fit of insanity before he tried to inform him of Walter's duplicity and real mission for Judge Dredd.
Downfall and Death
Cal takes pride in his "achievements" with Mega-City One, seeing it as a crime-free and efficient town. Judge Cal experiences hallucinations that prompt him to take drastic measures to preserve his achievements by gassing the entire city with Nerve Gas, allowing his Klegg mercenaries to leave the city before it happens. Judge Dredd moves into action, attempting to reverse Cal's brainwashing with their own briefing tape and starting a rebellion among the Judges who completely obliterate the escaping Klegg. In the face of this insurrection, Judge Cal flees to the Statue of Judgement and barricades himself in while he prepares the nerve gas, having his closest aides unknowingly take the poison first. When Judge Dredd confronts Cal on the top of the Statue of Judgement, Cal shows that his subliminal messaging still works and orders the Judges to apprehend Dredd. Before he can unleash the gas, Judge Dredd's underworld friend Fergee grabs Judge Cal and plummets to the ground, killing them both and bring an end to Judge Cal's reign of madness.
Legacy and later appearances
Judge Cal's influences continued to be felt well beyond his short tenure as Chief Judge, in no small part due to the death toll he incurred. The massive wall he constructed to keep the citizens in Mega-City One was retained as a defensive barrier as well as a way to separate Mega-City One from the Cursed Earth. Even decades later in 2117, Judge Dredd has to deal with a remnant of Judge Cal's time as the head of the SJS when the head of the Public Surveillance Unit, Judge Edgar, passes to Dredd a secret collection of files that Judge Cal amassed containing his blackmail on many judges. The Judges later reprimand Judge Edgar for secretly withholding the files, presumably for her own benefit and power much like Judge Cal.
Notably, a version of Judge Cal from an alternate universe where he successfully defeated Judge Dredd appeared in the story "Helter Skelter" (Progs 1250-1261) where he led a team of Dredd's villains from alternate universes who one way or another also defeated Judge Dredd. This alternate version of Judge Cal is able to seize control of the Hall of Justice, killing hundreds of Judges in the process and enacting a brief reign of terror before he is finally killed by Judge Dredd.