Short answers, pulled from the story.
Caracalla, born Lucius Septimius Bassianus on the 4th of April 188, ruled as Roman emperor from 198 to 217 AD. He was the elder son of Emperor Septimius Severus and Empress Julia Domna, a member of the Severan dynasty, and became sole emperor after ordering the murder of his brother Geta in December 211.
The Edict of Caracalla, formally the Constitutio Antoniniana, was issued in 212 and granted full Roman citizenship to all free inhabitants of the Roman Empire, excluding the dediticii and freed slaves. Before the edict, only roughly four to seven percent of all people in the empire held Roman citizenship at the time of Augustus' death in AD 14.
According to the 4th-century historian Aurelius Victor in his Epitome de Caesaribus, Caracalla acquired his nickname from a Gallic hooded tunic he habitually wore and made fashionable, possibly first donning it during campaigns on the Rhine and Danube. The writer Cassius Dio preferred to call him "Tarautas", after a famously diminutive and violent gladiator of the era.
The Baths of Caracalla were a massive public bathing complex in Rome, the second largest ever built in ancient Rome, covering around 50 acres (approximately 202,000 square metres) and capable of accommodating around 1,600 bathers at once. Construction began in 211 and included swimming pools, exercise yards, a stadium, steam rooms, libraries, meeting rooms, and fountains set within formal gardens.
Caracalla was stabbed on the 8th of April 217 by a soldier named Justin Martialis while travelling on the road from Edessa to Carrhae. Martialis had a personal grievance over Caracalla's refusal to promote him to centurion, but the praetorian prefect Macrinus is believed to have arranged the assassination. Macrinus declared himself emperor three days later with the support of the Roman army.
Caracalla introduced the antoninianus in 215 as a coin intended to serve as a double denarius, in part to fund large pay raises he had granted to the military. The coin had a silver purity of around 52% between 215 and 217 but its actual metal content was closer to one and a half denarii, causing people to hoard the older, purer denarii and worsening inflation.