Short answers, pulled from the story.
Marcus Vipsanius Agrippa was a Roman general and statesman born around 63 BC who served as the closest friend, son-in-law, and lieutenant of the emperor Augustus. He commanded the victorious fleet at the Battle of Actium in 31 BC, built Rome's original Pantheon, reformed its water supply as the first Curator Aquarum, and was granted constitutional powers nearly equal to those of Augustus himself.
Agrippa commanded Octavian's fleet at the Battle of Actium on the 2nd of September 31 BC, and Octavian's victory, which gave him mastery of Rome and the empire, was mainly due to Agrippa. In the days before the battle, Agrippa also advised Octavian to fight immediately rather than allow Antony and Cleopatra to escape, counsel that proved decisive.
Agrippa built and dedicated the original Pantheon in commemoration of the Battle of Actium during his third consulship. That building was destroyed in AD 80. Emperor Hadrian built the Pantheon that survives today, around 125, using Agrippa's design, and preserved Agrippa's inscription on the later building.
From 18 BC onward, Agrippa held proconsular imperium over both imperial and senatorial provinces and was granted tribunicia potestas, the powers of a tribune of the plebeians, without holding the office. These powers gave him veto authority over the Senate, the right to present laws to the People, and the sacred legal status of a tribune. He was, on paper, almost as powerful as Augustus.
Agrippa married three times: first Caecilia Pomponia Attica around 37 BC, then Claudia Marcella Major in 28 BC, and finally Julia the Elder, daughter of Augustus, in 21 BC. His children with Julia the Elder included Gaius Caesar and Lucius Caesar, both adopted by Augustus as heirs, and Vipsania Agrippina, who was the mother of the emperor Caligula and maternal grandmother of Nero.
Agrippa died in Campania in 12 BC at the age of 50-51. Although he had built a tomb for himself, Augustus had his remains placed in the Mausoleum of Augustus. Augustus honoured him with a magnificent funeral and spent over a month in mourning, and also oversaw the personal education of Agrippa's children.