Having been brought up by the Empress Elisabeth, at the age of seven he was a virtual stranger to his mother, Catherine the Great. As Tsarevich, he was kept in constant terror, fearing and mistrusting his mother. 
His first mistress was Katharina Ivanovna Nelidov (1758-1839), a lady-in-waiting to Paul's first wife. When this first wife died in childbirth, Catherine the Great ordered the removal of Katharina 
Nelidov. She went, but soon returned, and Paul's second wife accepted her presence. This affaire seems to have lasted a very long time, but she was replaced by Princess Anna Petrovna Gagarina (1777-1805). At the same time Paul amused himself with other ladies. He had a son by Sofia Ivanovna Levtsjina while Pelagina Vackar produced a daughter, Maria (1801-1803), but by the time she was born Paul had been killed. 
He lived away from St.Petersburg and formed an army of several thousand soldiers dressed in Prussian uniforms and drilled by himself. His four sons were to share this obsession with uniforms, parades, gaiter-buttons and other trivialities. 
Catherine the Great wanted to by-pass her son to have Paul's eldest son, Alexander, succeed her. Alexander guardedly consented but Catherine's death prevented this from happening. Without grieving for his mother, Paul took possession of her papers and burnt many of them. Aged forty-two and at last free from his mother, he declared a law in regards to the succession; from now on it would go according to the principle of male primogeniture, and no longer could a Tsar nominate his own heir. 
He appeared impulsive, erratic and irritable. He became a bogeyman and laughing-stock and was even rumoured to be mad. His dislike was directed at the gentry who were no longer safe from flogging, nostril-slitting, and the cutting out of tongues which, previously, had been preserved for peasants only. 
Paul was feared though small and ugly, in contrast with his tall and handsome children, with the one exception of Constantine. He started to plot against his children with plans of imprisonment in 
fortresses or convents. 
With the knowledge of Paul's eldest son, Alexander, several plotters met for a supper party. Nikita Panin, a disgraced statesman, and Count Alexander Pahlen, the military governor of St.Petersburg, 
were the main plotters even though neither took active part in the assassination. Some were drunk yet still gained access to the Tsar's residence where Paul was awakened by the noise they created. 
It was never made clear what happened, but in the end it seemed he was strangled with a scarf. One of the assassins, General Bennigsen, ensured that the Tsar was dead and dressed him in uniform. Officially he had died of an apoplectic fit, but this was not believed as the conspirators had already boasted about their deed. Consequently the people of St.Petersburg rejoiced and even strangers would kiss each other as though it were Easter; and by nightfall all available champagne had been drunk. 
 

Source: Leo van de Pas