Born in 15 in the Roman outpost that would one day become Cologne, she was the sister of Caligula.
She was married to Gnaeus Domitius Ahenobarbus (her second cousin and a man of distinction). She had a son with him (Nero) and then in 39AD, she murdered Gnaeus.
She was then involved in a plot to murder Caligula (her brother who was emperor at this point) with Marcus Lepidus (Her sister Drusilla's widower). The plot was discovered, Lepidus was executed (thanks to Agrippina betraying him to Caligula) and Agrippina was exiled to the Pontine Isles.
Following Caligula's assassination in 41, Agrippina was released from her exile by the newly crowned emperor Claudius (her uncle).
In 48, when Messalina (Claudius's wife) was executed for treason and adultery, she married Claudius. Through charm and manipulation she eventually convinced Claudius to place her son Nero as heir to the throne. She then arranged Claudius's poisoning and Nero's ascension.
To ensure that Nero's claim to the throne would be secure, she had Claudius's son by Messalina, Brittanicus poisoned at a banquet. She exerted her authority over Nero and manipulated him to ensure power for herself. But her rule over him was short lived. He confined her to her villa in Neapolis in 59.
Then Nero arranged an assassination attempt. During a festival, he offered to meet her on an isle in the bay of Neapolis. He rigged the sails on her yatch to fall and it almost killed her. She swam to shore however and survived. But Nero was not fazed, he sent in soldiers to meet her on the shore and finish the job. Her head was presented to Nero in Rome.
Her efforts and tutelage turned Nero into one of the most bloodthirsty and ruthless emperors in history. He also began the persecution of Christians and it is in fact Nero's greatest legacy.
The saying "Behind every great man are great parents" is also true for evil people: "Behind every awful evil person are evil parents." and behind Nero was Agrippina.