Short answers, pulled from the story.
Quintus Aemilius Laetus was a Roman military officer who served as praetorian prefect under the emperors Commodus and Pertinax in the late 2nd century CE. He is best known for his central role in the assassination of Commodus on the 31st of December 192 CE and for his involvement in the subsequent political turmoil of the Year of the Five Emperors.
Quintus Aemilius Laetus was born in Thaenae, in the Roman province of Africa, a city that corresponds to modern-day Sfax, Tunisia. His family was originally non-Roman and had obtained Roman citizenship in earlier generations.
Laetus was one of three conspirators who plotted and carried out the assassination of Commodus on the 31st of December 192 CE. He acted alongside the chamberlain Eclectus and the emperor's mistress Marcia.
Pertinax angered the Praetorian Guard by attempting to restore strict military discipline and by only partially fulfilling the financial payments the soldiers had expected. When the Guard rebelled on the 28th of March 193 CE, Laetus is reported to have withdrawn his support and deserted Pertinax, who was then assassinated.
Laetus was executed in 193 CE on the orders of Septimius Severus, who marched on Rome to seize power. Severus viewed Laetus as a potential threat because of his involvement in the killing of Commodus and in the auction of the imperial title to Didius Julianus.
Laetus appears as a key antagonist in the 2005 PlayStation 2 video game Colosseum: Road to Freedom. A character named Quintus in the 2000 film Gladiator, portrayed by Tomas Arana, is also loosely based on Laetus, serving as a Praetorian Guard officer.