Tarquinius Superbus

Kill your wife and become king
Lucius Tarquinius Superbus (the proud) was the seventh and last of the Roman kings.
Tarquinius story starts with him murdering his first wife Tullia. Simultaneously her sister (also named Tullia) murdered her husband (his brother). Apparently unsuspected, these two then got married. Over the years Tullia talked into her husband that his throne had been stolen by her father Servius Tullius.
After Tullius had reigned for 44 years , he was murdered by Tarquinius and Tullia drove her chariot over her fathers dead body that was lying in the street.

A tyrant
Tarquinius Superbus seized the power by force, had his opponents in the senate murdered and reigned like a tyrant.

Sub doing of Gabii
His son Sextus Tarquinius first helped him in conquering Gabii by betrayal. He made the Gabians believe he had fled from his tyrannical father, won their trust and after some time had his opponents in Gabii executed. Then without a battle Gabii fell in Roman hands. Lucius built the  temple  of Jupiter  that his father had  promised on the Capitoline hill.

Sibylline books
Tarquinius Superbus bought the books from the Sibylle of Cumae. He claimed that she offered him 9 books for an exorbitant high price. When he tried to negotiate about that price, Sibylle tossed three of the books into the fire.
For the six remaining books she asked the same price  as she had asked for the nine books. When Tarquinius made a remark about this, again she threw three of the books into the fire.
And again she asked the same price. Fearing to have to leave empty handed, Tarquinius accepted and paid the price for three where he could have had nine books. More likely is that Tarquinius invented this story to defend himself why he had paid too much for the three books.
The books were kept in a room beneath the temple of Jupiter on the Capitoline hill. In times of great dangers these books were consulted by the decemviri (ten-men) in order to find out which religious measures had to be taken that would appease the gods.

Rape of Lucretia
Sextus fell in love with Lucretia, Collatinus' wife.  He showed this love  by raping her.  The next day she sent for her father and husband each together with an entrusted friend. As soon as  Spurius Lucretius with Publius Valerius and L. Tarquinius Collatinus with Lucius Junius Brutus had arrived she told them what had happened and made them swear to revenge her.  After they did so  she killed herself  with a knife.
The men decided to expel the royal family.
Tarquinius at that moment was waging a war and when he returned he found the gates of Rome closed.