Klavier Gavin is Apollo Justice's rival. He is the younger brother of Justice's former mentor, Kristoph Gavin. He was also the lead vocalist and guitarist of his own rock band, the Gavinners.
Klavier Gavin trained to become a prosecutor in Germany. He was touted as a genius, a "true thoroughbred of the prosecutor's office", which helped to propel him to his first trial at the age of 17, sparring with the renowned defense attorney Phoenix Wright.
Before the trial took place, Klavier's older brother, Kristoph, told him that Wright was going to present false evidence in court and gave him a witness to testify as such. Convinced that Wright was a fraud, Klavier engaged Wright rudely and taunted and cornered him until he came up with the fake evidence. Klavier sprang his trap, and Wright was exposed as a fraud. However, the defendant disappeared from the courtroom, and no verdict was given. Wright would later lose his badge in a hearing with his fellow defense attorneys. Klavier always wondered how his brother knew about the forgery ahead of time but never questioned him for the next seven years.
Seven years after Wright's disbarment, Apollo Justice got Kristoph Gavin convicted for murder. Intrigued, Klavier faced Justice in his next trial to test the young attorney's true worth. Justice eventually convinced Klavier that he had the wrong suspect on trial, and Klavier turned to guide Justice through the process of implicating the real criminal, causing Justice to wonder whether he really had "won" the case.
Klavier then invited Justice and Trucy Wright to one of his concerts, in which he was to perform with a well-known Borginian singer, Lamiroir. However, it was not a good day for Klavier. First his keys were stolen, forcing him to take a taxi to the concert and break open his guitar case. Second, during his performance with Lamiroir, his guitar burst into flames for no apparent reason. Finally, to round off the whole fiasco, Lamiroir's bodyguard was shot dead with his own revolver. Justice and Klavier faced off in court again, and Lamiroir named the Gavinners' second guitar, Daryan Crescend, as the killer. Refusing to believe it at first, he eventually came to grips with the truth and guided Justice again to finding the evidence.
Three months later, Klavier participated in Phoenix Wright's test trial for the Jurist System, which involved the poisoning death of Drew Misham, with his daughter Vera Misham as the defendant. The case's connection to Klavier's first case came to light, and Klavier was forced to face the past. His brother Kristoph was summoned from his cell as a special witness, accused of being the real killer. Klavier wanted to believe in his brother, but Kristoph tried to bluff his way out of his predicament, and Klavier finally came to accept the truth. Once again, Justice and Klavier worked together to piece together the circumstances and motives behind the crime at hand, but they could not conclusively prove Kristoph's involvement in the forgery that had ended Phoenix Wright's career. Nonetheless, Klavier remembered that the jury, not the judge, had the power to decide the defendant's fate. When Kristoph found out about the jury, he was furious at the prospect of his plan being nullified by common people. Klavier told his brother that the law no longer needed him, and the jury declared the defendant innocent of the murder.
Klavier started his rock band some time before he started his law career. His band's first single went platinum overnight.
Seven years after kicking off his double career, Klavier visited Borginia. He met Lamiroir there and was entranced by her voice, calling it "divine". He invited her to sing in one of his concerts, and he also received a guitar. Lamiroir and Klavier performed a duet for the concert (the concert to which he had invited Justice), but the guitar caught fire during the song, and Lamiroir's bodyguard was also killed. Distraught by these events and the conviction of Crescend for the murder, Klavier vowed never to sing the song again.
The jury trial in which Klavier saw Kristoph implicated as the killer affected Klavier so deeply that he decided to disband the Gavinners and pursue his law career more fully.