Not much else has been revealed about his past, but he once visited Tsuna when the latter was a child. It is implied that he has led the Vongola for a long time, as a flashback in the manga shows that he was considerably younger than he is now when he inherited the position from his mother.
In his old age, Timoteo became aware of a mentally ill woman who mistakenly believed he had fathered a child by her. This child turned out to be Xanxus, a Flame of Wrath user, who would eventually become the leader of the Varia. Xanxus' mother brought her son to meet Timoteo and upon witnessing a demonstration of the boy's exceedingly rare Flame, Timoteo decided to adopt him.
Eight years prior to the Varia Arc, Xanxus read Timoteo's diary and found out that he is not Timoteo's son, therefore has no legitimate claim to leadership of the Vongola. He then planned a coup d'état, or an attempt to overthrow Timoteo. This became known as the largest coup d'état in Vongola history, and was nicknamed the "Cradle Affair." During this time, Xanxus and Timoteo were forced into battle, with Timoteo sealing Xanxus through the Zero Point Breakthrough: First Edition. It has since been revealed that Timoteo knew about the coup beforehand, because Ottavio, the late former vice-captain of the Varia, had warned him about it.
At some point, he tried testing Gokudera's loyalty to Tsuna by making it seem as if Gokudera would only get promoted if he (Gokudera) returned to Italy. Gokudera passed the test and stayed in Japan after realizing that Tsuna truly values his friendship and doesn't just see him as a right-hand man. Timoteo had ordered Dino to kill Gokudera if he had shown up, but Dino had no intention of doing so and instead had planned to hide Gokudera overseas. Fortunately, Yamamoto went in Gokudera's stead and spent some time in Italy with Dino, who was relieved at not having to obey Timoteo's order to kill Gokudera.
He accepted Iemitsu's son, Tsuna, as the next Boss of the Vongola Famiglia, but a fake ninth replaced him and decided that Xanxus was more worthy to become the next Boss. Not realizing that this Ninth was a fake, Iemitsu argued, wanting Tsuna to become the 10th Boss. Thus, the fake ninth sanctioned the traditional Vongola battle; those who wield the same Ring would have a one-on-one battle. The real ninth was kidnapped by Xanxus who had placed him within a Gola Moska, thus draining him of his life energy. When Tsuna sliced the Gola Moska's armor in half, freeing him, the Ninth was able to use his Flame to show Tsuna his past.
In the Future, he had been unaccounted for since the Millefiore Famiglia raided the Vongola Headquarters. During Tsuna's training within Hibari's spiked ball, he appears in a vision with the other Vongola Bosses and is shown with a Sky Flame Sceptre, his signature Dying Will Flame Weapon. Seeing him in the vision causes Tsuna to believe that he may be dead.
He knew about Tsuna's battle with Byakuran in the future from the Arcobaleno's memory transmission. Five days before the Inheritance Ceremony, he arrived in the Japan airport saying that he looked forward to seeing Tsuna. His Storm Guardian and right-hand man, Coyote Nougat, replied that he had been saying that a lot. While staying at a hotel in Japan, Timoteo's Vongola Guardians were seen standing in front of Timoteo, and Timoteo's Storm Guardian and Thunder Guardian informed him that an allied Famiglia had found out who was plotting to interfere with the ceremony and that the same Family will take care of the group as a gift to the next Vongola Boss. He later invited Tsuna to his hotel room to talk. There, he revealed that he knew all about the Future from a dream sent by Uni. He began trying to convince Tsuna that he wasn't meant to be a Mafia Boss, but to lead the conversion of the cruel Vongola to the way it once was, a group helping others.
After Tsuna's departure, Timoteo revealed to Reborn the treasure passed to each Boss, which was a cylinder which he calls the Vongola Sin. The next day, Tsuna went back to the hotel to give his final opinion to become the boss of the Vongola Famiglia. Tsuna turned down the offer because he thought that the Mafia world was too big and that he wanted to treasure the time he spent with his friends. Timoteo had already expected Tsuna's decision to turn down the position of being Boss and accepted it. He told Tsuna that he was sure that he would do well in life, and he should have more confidence in himself; however, he also tells him that he still hadn't given up on the idea; Reborn, however, felt that the Ninth went easy on Tsuna. However, after hearing that Yamamoto was in the hospital, Tsuna agreed to put the ceremony back on so he could find the culprit.
Thanks to the Ninth's swift judgment, Yamamoto's condition wasn't leaked to the press, police, or to the other Families, though the Ninth did agree that Yamamoto should go to the ceremony as an Illusion to prevent any rumors from spreading. Reborn said it would be a secret between the Ninth and Tenth generation. The next day, at the Inheritance Ceremony, Timoteo was seen handing the Sin down to Tsuna, when suddenly, a loud noise started to be heard, followed by an explosion. After the explosion, Timoteo is seem to have hurt his arm, but dismisses it as a scratch. He then told everyone to seal the exits, and to not let anyone escape. Reborn said that the culprit's objective was to destroy the Sin. The Ninth reassures Tsuna that it was a mere replica of the Sin in order to lure out the culprit. He proclaimed that the real one was in a vault in the next room, protected by all seven of the Ninth generation's Flames that was impossible to penetrate or be destroyed by any weapon. The Ninth tells Tsuna that they would find the culprit and that he would take full responsibility for what has been done to Yamamoto. Suddenly, Ganauche III tells the Ninth that the vault has been broken into. The vault door reveals that the Simon Famiglia are the culprits. Their appearance surprises everyone. Enma says that they have come to take back the Sin for the Simon Family, which shocked everyone again. He than pours the contents of the Sin onto his ring and goes into Hyper Dying Will Mode, and his arm mutated into what appears to be a gauntlet. Tsuna, who was outraged by this, also enters Hyper Dying Will Mode and prepared to battle him. When Tsuna asks why they attacked Yamamoto, Enma responds that he was a Vongola Guardian and it was a "rightful atonement." Adelheid also say that it was because he found out their plans for the ceremony and that Yamamoto saw the Simon Rings. This surprises everyone, Reborn even said that even hasn't heard about the Simon Rings. Adelheid Suzuki says that just recently that found the rings, when the earthquake uncover them under Simon Cozzato's grave. Enma then went on to explain that the Sin belonged to the Simon Famiglia and that it was the blood of their first boss. Its revealed the one way to restore power to the rings. Reborn asks the Ninth if this is true, but Timoteo says that he has never heard of a such thing before. He proclaims that when he received "Sin" from the pervious boss, Vongola Ottavo, she told him that "this is war blood that must never be forgotten." Adelheid however says that the real reason why no one in the Vongola knows about Sin anymore was because "Your ancestors tried to hide the truth." Adelheid tells the story that during Vongola Primo's time, the First boss of the Simon Famiglia was betrayed the Primo. Timoteo says he never heard that story and that even though the Simon was close to them, they "disappeared overseas on their own accord." Julie Kato replies, "We thought you'd say that~" and that they "Never heard of it~." Enma then asks Tsuna if he's ever heard the story, which Tsuna replies, "I don't deny that the blood of the Vongola runs within me." Neither do I have the ability to really find out what happened between Vongola and Simon. I can't prove that it didn't happen. But there is one thing I can swear on my grave. Vongola Primo is man who would never do such a thing!" This angers Simon and they make the declaration that Enma will inherit their family as the tenth boss and take revenge of the Vongola by gathering mafia from all over the world and standing above them as leader. The purpose of the war being to gain back the pride of Simon. Adelheid and the others then release their rings as Enma says that the reason that Vongola Primo got rid of Simon was because they had a power that rivaled the Seven Flames of the Sky, which is the Seven Flames of the Earth. Enma quickly defeats all of Tsuna's Guardians, breaks the Vongola Rings, and leaves.
Timoteo quickly calls for help, and Squalo asks the Ninth permission to take out the Simon Famiglia, but he is denied that. The Ninth says that can't create more victims, since their abilites lies within the Simon Rings, that they know nothing about. Timoteo takes full responsibilty for the whole ceremony, and blames himself for not uncovering the truth about "Sin." But suddenly Talbot, an old acquaintance of the Ninth, who has been rumored to have worked for the Vongola during the Primo time, offers to repair the rings. Talbot proclaims that the only way to match the Simon in power is to upgrade them with blood of the Primo, called Penalty. The sudden news shocks them all, in which the Ninth asks why Talbot has the blood of the Primo, but Talbot replies that he doesn't remember the details of the past. Talbot asks Tsuna if he wants the upgrade, Tsuna agrees. After Tsuna agreed for the Upgrade, Talbot asks for spare room below, to create the new rings. While Talbot upgrades the Vongola Rings, Gokudera, Ryohei, Tsuna, and Timoteo wait in the a room to rest. Talbot then presents the new rings, but they are in seven jagged rocks. Talbot replies that these are one stage from the new Vongola Rings, and to unlock them the they must prove their resolve. After everyone has unlocked their new gear, Timoteo starts meeting, to deal with the threat of the Simon Famiglia. Ganauche tells the Ninth, that all records about the Simon have been discarded after a certain time period. But they where able to locate the family base, in some letters written by Simon Cozzato to Primo. Timoteo proclaims that they must be stronger than the Simon in seven days, and that they must gather up their forces.
Tsuna asks the Ninth that he alone wants to fight the Simon since he believes that this isn't a battle between the two Famiglia, and that he and Enma are alike. Squalo, however, tells Tsuna that it was a Mafia war and gets into argument with him. The Ninth silences them, and claims that since the Ceremony was cancelled, he was still the boss of the Famiglia. Timoteo allows the matter at hand, the duty to stop the Simon, up to Decimo and his Guardians. But, he does tell Tsuna that Reborn must go with them; however, the Ninth forbids Reborn from attacking the Simon. Timoteo tells Ganauche to prepare a ship for Tsuna and his Guardians. Nie Brow Jr. informs the Ninth about Simon's background about how they all lost their family at an early age, but was concerned about Enma's case because his was more different. When Nie Brow Jr. reminded Timoteo about the Flood of Blood incident, Timoteo was shocked and knew something about the incident.