Moses Smith attacked 26-year-old Abdi Mohamed outside Easy4insurance, in Upper High Street on June 8, 2021, Wolverhampton Crown Court heard.
He was airlifted to the Queen Elizabeth Hospital in Birmingham but died later that day.
Smith, 40, of Lindon Road, Brownhills, denied an offence of murder and pleaded guilty to the lesser charge of manslaughter on grounds of diminished responsibility.
The Crown Prosecution Service had previously accepted his guilty plea.
Mr Edward Brown KC, prosecuting, said Smith had been in touch with the insurance firm on a number of occasions in the period leading up to the attack, and was a customer.
He told the court on Friday that Smith believed the company had defrauded him of his savings, but there was no evidence of this.
On June 8, 2021, Smith bought a knife, drove his van to outside the offices of the firm and asked Mr Mohamed to come to the van with him to inspect some apparent damage.
He stabbed the victim a number of times in a "frenzied, determined and terrifying attack", Mr Brown said.
He said a few weeks beforehand he had visited the office and was described as being "scruffy, smelly and swearing", and people thought he was suffering from mental health problems.
On the morning of the attack, Smith called the insurance firm twice asking for Mr Mohamed, before going to the building itself at around 12.10pm.
Smith spoke to Mr Mohamed about apparent scratches on his van and whether it was worth claiming on his insurance.
Smith then asked him to go with him to inspect the damage and it was then he launched his attack, which lasted around a minute.
Investigations revealed he had previously bought a kitchen knife in Brownhills.
Mr Brown said: "The attack was frenzied, completely unprovoked and carried out without any warning at all. It was a truly terrible and determined attack.
"With no warning at all the defendant produced the knife and began plunging it repeatedly into Mr Mohamed's upper body.
"The defendant continued to stab the deceased as he fell to the ground and then began kicking him."
Smith accused him of "ruining his life", the court heard.
Two people from nearby shops rushed out and intervened and Smith drove away. He then went to Bloxwich Police Station during the afternoon, claiming he had been in a fight.
Officers seized Smith's phone and found he had searched the internet about 'revenge', the insurance firm, whether it was possible to go to jail for fighting and how many years people are sent to jail for murder.
Mr Mohamed suffered deep wounds to his neck and went into cardiac arrest as he was rushed to hospital. He was given emergency surgery, but died later that day.
Mr Brown said he was "well liked and well regarded" in the insurance company and those who knew him were "devastated" by his death.
A victim impact statement representing his family, which was read to the court, said "it was the most devastating of days" and his parents had "lost the light of their eyes".
It said: "Our hearts were broken and shattered into pieces. How does an innocent person go to work and not return."
Mr Brown added: "They ask the question who is safe when a killer is able to come to someone's workplace."
Mr Mohamed's family described him as having a "beautiful personality", always having a smile on his face and described Smith as a "monster".
They said a community centre had been built in his name thanks to generous donations, allowing his legacy to continue.
The statement added: "He was the light of our life and his loss is a dark cloud over us all, life will never be the same without him."
Defending Smith, Mr Trevor Burke KC said he had walked into Bloxwich Police Station and surrendered himself, and had no history of violence at the time.
Sentencing Smith, Judge Michael Chambers KC said he had subjected Mr Mohamed to a "brutal and repeated attack".
He told him: "You stabbed him, clearly intending to kill him."
The judge handed him a life sentence and said he would have to serve a minimum of 12 years.
Speaking after the case, Detective Inspector Michelle Thurgood, from force CID at West Midlands Police, said: "Our thoughts remain with Mr Mohamed's family, who have been left devastated by what Smith did and unfortunately despite Smith's plea, they are still without any real explanation for what happened."