Short answers, pulled from the story.
Lucius Antonius was the younger brother of Mark Antony and a consistent supporter of his political career. He was the son of Marcus Antonius Creticus and Julia, who was a third cousin of Julius Caesar, placing the family at the heart of late republican Roman politics.
Pietas was a Latin word conveying duty, loyalty, and devotion to family. Lucius Antonius was given this nickname as a young man, and his political career consistently reflected it through his steadfast support of his brother Mark Antony.
As tribune of the plebs in 44 BC, the year of Caesar's assassination, Lucius Antonius brought forward a law authorizing Julius Caesar to nominate the chief magistrates during Caesar's absence from Rome. He also proposed a separate agrarian law in favor of ordinary Romans and Caesar's veterans.
In 41 BC, during his consulship, Lucius Antonius and his sister-in-law Fulvia raised an eight-legion army to oppose Octavian's policies, particularly the forced land redistribution. He marched on Rome, drove out Lepidus, and pledged to abolish the triumvirate before being forced back to Perusia in Etruria, where he was besieged by three armies and surrendered in the winter of 41 BC.
After Perusia fell and Lucius Antonius surrendered, Octavian spared his life. He was sent to Spain as governor. The date and circumstances of his death are entirely unknown.
Cicero gave a highly unfavorable view of Lucius Antonius's character in his Philippics. The source notes that Cicero was motivated in large part by personal animosity in writing that portrait.