Theodore "Tio" Osmond was a drug dealer that operated in Farmington. He started being the right-hand of Vic Mackey's protege Rondell Robinson. However, when Rondell started to lose control, Tio started plotting to take control. Eventually, Mackey chose him as Rondell's replacement and offered Tio protection for a fee. Tio used his comic book store as a front for his drug dealing business.
When Armadillo Quintero started eliminating rivals to consolidate the Latino gangs, he burned Tio's store. This prompted Tio to seek hiding. However, he still was captured by Armadillo who murdered him by "firenecklacing". Tio had a young daughter.
Tio Osmond was Rondell Robinson's right-hand man. However, when Rondell started using his own drugs and telling people that he was protected by Vic Mackey and Kern Little, Tio started looking for ways to take his place. One day, when Rondell was with Kern Little, Tio and some of his men approached their car and started shooting at them trying to kill Rondell. However, they were unsuccessful since Kern's car was armored.
Later that day, Shane Vendrell and Ronnie Gardocki arrested Tio when they found him dealing Rondell's drugs without his permission. They brought him to the Barn for questioning, and he told Vic that things had to change because Rondell's behavior was endangering the business. Although Vic was reluctant at first, eventually, he decided that Tio was right. He returned to question him and asked him why he would be a better dealer for him. Tio told him that Rondell was becoming sloppy due to the drug use. He also told him Rondell was telling everybody about him being protected, and then told Vic how he would've dealt with the Nation of Islam. He then brought up the subject of the "rent" and they agreed on $50,000 for protection.
Several days after, Tio was on a corner supervising his dealers when Vic Mackey approached him to ask his help. They told him to ask around if anybody boasted about shooting police officers. Some hours later, Tio told Vic that he knew one of the murderers because his father was a frequent drug user. He then gave Mackey his address. Some hours later, Vic and the Strike Team approached Tio again to ask him for some money. They wanted to use the money to pay potential witnesses that might've seen the other two shooters around. Reluctantly, Tio gave them what he had.
Tio went with the Strike Team to pick up a shipment of cocaine that Jasper had brought him. Tio inspected the product and decided it was good. He then left with his men, with Shane and the Strike Team close behind. However, on the road, they were stopped by a sheriff who found the drugs in the trunk. While they lay on the ground, Shane stopped and told the officers that they were supervising a raid and that Tio was their informant. After verifying with Vic Mackey and Captain David Aceveda, the sheriff let Tio and his men leave.
The next day, Tio called Vic to tell him that the drug they had bought was bad. Vic stopped by Tio's lab and he showed him how one of his men started vomiting blood after snorting some cocaine. After the men had a cardiac arrest, Tio ordered his men to get rid of the body. Vic then told him he would find who was messing with his drugs. When they brought Jasper to ask him if he was the one poisoning the drug, he told Tio and Vic that the drug came through a front business that belonged to Navaro Quintero.
A few days later, Navaro's brother, Armadillo, had Tio's store burned. Afraid that he could be murdered, Tio decided to hide in the outskirts of the city in the house of the mother of his daughter. When Vic Mackey and Shane Vendrell visited him to see how he was and what he knew, he told them that fortunately he had taken most of the drugs out. However, he also told them he kept a safe in the back room of his store with some cash and an account ledger. Still, Tio assured Mackey that the ledger wouldn't lead to him since he referred to him with the code word "Landlord". Mackey then asked Tio for the names of some of his men to send a message to Armadillo by burning one of his buildings. Tio gave them the names so Shane could tell them what to do. Since Mackey left Shane alone, Tio offered his cell phone so he could call Lem to pick him up.
Vic then returned to Tio's house with Claudette Wyms, after he was unable to get rid of the safe. Before Claudette came into the house, Vic assured Tio that he would cover his back if Tio covered his. He then showed him an old picture of a felon called Ripley Verdugo to use as scapegoat for the store arson. When Wyms finally came in, Tio kissed his daughter and they brought him to the Barn for questioning.
As they brought him inside, Tio saw Armadillo in the cage and started screaming at him for burning his store. Claudette then took him to one of the interrogation rooms. When she showed him an old picture of Ripley, where he had his head shaved, Tio identified him saying that he "couldn't miss that inked bald head". Mackey told her he would pick Ripley up, but Claudette stayed with Tio to inquire about his records. Since he refused to talk, Claudette offered to ignore the incriminating ledger if he helped her convict Armadillo.
While Claudette was interrogating T.O., Vic interrupted her to tell her the Strike Team had brought Ripley. However, during her questioning, she noticed that Ripley wasn't bald anymore and realized that there was something going on. She returned to T.O. and pressed harder on him about who he was protecting. Since he still refused to talk, she unplugged the surveillance camera in the room and continued asking him if he was paying a cop for protection. At this moment, Captain Aceveda interrupted her and told her about a similar arson that could be related. While she went to investigate it, Aceveda and Mackey released Tio and gave him his ledger ordering him to burn it.
As he returned to his home, Tio realized that three of his best dealers were missing. Knowing that Armadillo might've gotten them, he contacted Vic. Mackey then told him to call the rest of his guys and tell them to lay low, but Tio wanted to get revenge on Armadillo. Mackey tried to calm him and left. That night, Armadillo and his men captured Tio and took him to an abandoned park. When they were about to "firenecklace" him, they had him call Mackey so he could listen to him scream. When Mackey answered the phone, Tio started screaming for him. He died after and his body was found by the police. Claudette Wyms was present at the scene of the crime.