Clayton Weatherston stood trial for the murder of Sophie Elliott on January 9 last year. He said he was guilty of manslaughter, but not murder and claimed he was provoked into killing her.

However, a jury found him guilty of murder.

Forensic psychiatrist Philip Brinded said during the trial that Weatherston suffered from a personality disorder and called him a "grossly narcissistic individual" without empathy or remorse.

And psychiatrist Dr David Chaplow, New Zealand's director of mental health, called Weatherston controlling and said he appeared to have an "inflated sense of his own achievements".

He said Weatherston was prone to narcissistic rage, often due to frustrations with his relationships.

Narcissistic personality disorder first appeared as a disorder in the Diagnostic and Statistical Manual of Mental Disorders in 1980. Prior to this, narcissism was not counted as an official disorder.

It usually manifests by late adolescence or early adulthood and is more prevalent among men than women.

The term stems from Greek mythology. Narcissus was a youth who rejected the nymph Echo and as punishment was doomed to fall in love with his own reflection.

Narcissism is a mental disorder in which people hold an inflated perception of their own importance and have a desperate need for admiration.

They may fantasise about power and success, exaggerate their achievements, and believe in their own superiority. They feel a sense of entitlement and have little regard for other people's feelings.

However, their self-esteem is fragile and narcissists usually have trouble accepting criticism.

They crave attention or approval, and often exhibit dramatic or emotional outbursts.

Narcissists often have a history of intense but short-term relationships and have difficulty forming genuine bonds with others.

Treatment is based around psychotherapy. However many narcissists never seek treatment or simply do not recognise problems with their own behaviour.

The causes of narcissistic personality disorder are not known. Some evidence suggests a dysfunctional childhood may be to blame, while other evidence points to genetics.

Other alleged narcissists from history
Saddam Hussein
Joseph Stalin
Adolf Hitler
Kim Jong Il
Charles Manson
Pol Pot
Benito Mussolini
Ted Bundy