Carlo Hesser had a successful underground drug-trafficking operation in Llanview until then-mayor Victoria Lord Buchanan stepped in to put a stop to his operations. Carlo's son, Johnny Dee, became determined to help his father and hired someone to scare off Viki, but instead it resulted in Viki ending up paralyzed for a long time.
Around the same time, Johnny Dee had also engaged in an affair with Viki's sister, Tina Lord Roberts. Tina then realized she was pregnant, she was unsure whether the baby's father was Johnny Dee or her estranged husband, Cord Roberts. A blood test later proved the father was Cord, but this only infuriated Johnny more. One day a furious Johnny kidnapped Tina and threatened to kidnap her. A paralyzed Viki transformed into Niki Smith, regained the use of her legs and killed Johnny in self defense. After learning of Johnny's death, Carlo vowed revenge against the Buchanans, no matter what!
Carlo kidnapped sisters Megan Gordon and Sarah Gordon Buchanan, the wife of Viki's brother in law Bo Buchanan, and sent them into Amish Country. Eventually the sisters managed to escape, but Carlo managed to kidnap Sarah once again. Bo Buchanan then hired former FBI agent Alex Olanov to help him track down Sarah.. Alex eventually discovered her whereabouts and struck a deal with Carlo: his freedom in exchange for releasing Sarah. Carlo agreed, but while en route to Llanview, Sarah's plane crashed and she was presumed dead. The Buchanans blamed Carlo and their feud intensified.
Carlo then started blackmailing Tina's friend, Gabrielle Medina, to be a part of his wayward plots. Carlo and Gabrielle planned to drug Viki in order to turn her into Niki and have her kill her own daughter, but Gabrielle backed out at the last minute and was forced to testify against Carlo. When Carlo threatened to hurt Gabrielle's son, Al Holden, Gabrielle was forced to take the blame for the plot. The Buchanans continued to search for ways to catch Carlo in the act and for this they turned to Alex, who by this time was in jail after trying to drown Bo's girlfriend, Cassie Callison. Alex was to get incriminating evidence against Carlo in exchange for her freedom, but little did they know that Alex had ulterior motives. Alex also made a deal with Carlo that if he were to marry her, she would destroy all the evidence that she had collected against him. Carlo reluctantly married Alex and as his wife she wasn't forced to testify against him. Carlo and Alex soon turned into lovers and engaged in kinky sex and the two were inseparable...for the time being.
On Bo's wedding day to Cassie, Alex found a very much alive Sarah Buchanan and brought her to the reception where she was reunited with her shocked family. Carlo, it turned out, had been holding her captive. Sarah soon became obsessed that she had witnessed a murder during her time in captivity. Things got even more complicated when Carlo's lifeless body was found in Max Holden's house. It seemed almost everyone had a reason to want him dead and Sarah was the main suspect. It was later revealed that Carlo's niece, Stephanie Hobart, was the actual killer. Stephanie confessed that she had learned that Carlo had murdered her father, Joseph. Joseph was an FBI informant, and Carlo had murdered his adopted brother in order to cover up his tracks. After learning this, Stephanie killed her uncle in an act of revenge. This was the murder that Sarah had witnessed. Alex, in loyalty to the Hesser family, eventually had Stephanie flown to Mexico in order to avoid prosecution. Carlo's reign of terror had come to an end. Or so it seemed.
Alex became the kingpin of Carlo's mob empire, but she soon found the power slipping away. To her luck, Alex found Mortimer Bern, an Egyptologist who was the spitting image of Alex's late husband. Alex decided to transform Mortimer into Carlo, but she soon realized that wouldn't be an easy task considering they were total opposites. But Alex was determined, and Mortimer slowly started to transform into Carlo. The transformation was so successful that Mortimer began to act like Carlo all the time and even became obsessed with one of Carlo's ex flames, Renee Divine.
Eventually Mortimer got out of control and there was nothing Alex could do to stop him, except have mommy dearest drop in for a visit. Mortimer's mother, Wilma Bern, arrived in town and revealed that Mortimer and Carlo were actually twin brothers, separated at birth. Mortimer finally came to his senses and realized he had become his brother. In order to correct his behavior, Mortimer said goodbye to Alex, Renee and Carlo's empire and left Llanview.
In 1996, Asa ventured into business with a mysterious man known as "Poseidon." Alex, who was now married to Asa, became curious and soon discovered that "Poseidon" was none other than Carlo Hesser! Alex and Carlo secretly reunited, and Carlo managed to trick Asa into giving him $30 million.
Carlo resurfaced in Llanview and presented himself as reformed, in order to avoid trouble. But after Alex had Carlo divorce her in order to be with Asa, Carlo got mad. Carlo teamed up with local criminal R.J. Gannon and the two caused trouble for the Buchanans. Carlo looked for someone worthy to take his place, and he chose former gang leader Antonio Vega to be his heir. Several events forced Antonio to turn to Carlo for help and Carlo made him his surrogate son. Carlo hatched up another plot of revenge against Viki and hired Elliot Durbin to convince Viki to kill her son Kevin. After Elliot failed, Carlo had him killed. Carlo was also looking for revenge against Max, who made Carlo think he was dying in order to give up the money he stole from Asa. At this time, Alex had also left Asa and made Carlo think she was pregnant, but on their wedding night, a furious Asa exposed Alex to Carlo. Todd was also seeking vengeance, after all Carlo was responsible for him being shot in Ireland. It seemed everyone had a reason to want Carlo dead, again.
At a Llanview gathering on a yacht, Carlo was found dead by Blair Cramer with a bullet hole in his head. Everybody was a suspect, but it was Antonio who seemed to be heading up the list. Mortimer returned to town as a witness. It was then revealed that Alex had shot and killed Carlo. Mortimer then disappeared with Asa's $30 million. He later returned and lured Alex away, although many wondered if Mortimer was actually Carlo in disguise. In 2001, Alex returned to town and said that Carlo had left her and disappeared with Asa's money. This meant the person whom Alex killed was actually Mortimer Bern.
Carlo popped up again briefly in 2005, this time at Asa's behest. When someone needed to take the fall for a plot against Blair, Carlo wound up in Statesville prison, where it was soon revealed that he was the criminal mastermind behind Cristian's captivity, as well as the person who brainwashed him into killing Tico Santi. He was instrumental in launching the 2005 riot at Statesville prison, but was unsuccessful in escaping and remained incarcerated.
Carlo resurfaced three years later, this time in the European principality of Mendorra, where he came face to face with the daughter no one knew he had: Llanview police officer Talia Sahid. Days earlier, Talia had inexplicably aided Jonas Chamberlain, the sinister U.S. Ambassador to Mendorra, in kidnapping her roommate Sarah Roberts. Soon Antonio and Cristian, who are dating Talia and Sarah respectively, discovered that Jonas had both women; they and Sarah's mother Tina Lord - who had been posing as the Crown Princess of Mendorra -accompanied Jonas back to Mendorra in order to make an exchange: Sarah and Talia for the Crown Jewels, which Tina had in her possession. Talia and Sarah were being held in a jail cell beneath the royal palace when in walked Carlo, who it turned out was the real mastermind behind the kidnappings. He had disappeared from Statesville prison with the help of corrupt Llanview Police Commissioner Lee Ramsey.
Talia as it turned out was Carlo's youngest child; during her early childhood, she had lived under Carlo's tyrannical rule, tormented by her demented siblings, Johnny Dee and Charlotte. Eventually, Talia had escaped from Carlo with her mother. Taking her Syrian stepfather's last name "Sahid," Talia had eventually gone into law enforcement for the express purpose of repudiating all the evil done by Carlo, and in the hopes of eventually bringing her father to justice. Carlo intended to force Talia to marry Jonas, the true heir to the throne and Carlo's puppet. Talia protested and stalls, but went through with the royal wedding on July 31, 2008, to save Antonio and her friends from harm. Talia stayed behind as her friends returned to Llanview, but soon Antonio, Cristian and Sarah returned with a plan to free Talia. They drugged Carlo and Jonas and staged them in bed together, just as Talia lead a team of reporters to "discover" the scene on live television. With a protesting Carlo and Jonas arrested for fraud, Talia and the others left Mendorra. While awaiting for a connecting flight from New York City to Llanview, Cristian was kidnapped and awoke to find himself a prisoner on a cargo ship, with Carlo there gloating. Posing as his dead twin brother Mortimer Bern, Carlo delivered Cristian to Plato prison in Colombia, passing him off to the authorities as "the worst criminal in all of Colombia." Carlo then disappeared.