Final answer:
Nero's brutality was observed by contemporaries such as Burrus, who served as his advisor, and Galba, who became emperor after Nero. Their impressions of Nero's despotism would thus be firsthand, given their proximity to power and the subsequent events of the "Year of the Four Emperors".
Step-by-step explanation:
Nero's brutality was seen by many including his contemporaries Sextus Afranius Burrus, Aulus Vitellius, Otho, and Galba, all of whom had different roles and perspectives on his reign. Burrus, as the Praetorian prefect, initially served as an advisor and was part of Nero's close circle of power alongside Seneca.
However, as Nero's rule progressed towards tyranny, Burrus may have disapproved of Nero's methods, seeing them firsthand.
Galba and Otho were directly involved in the politics and power struggles of the time, with Galba eventually succeeding Nero as emperor, which indicates that he might have observed Nero's brutality during his reign.
However, the direct engagement of these figures with Nero's brutality varies; in the quote regarding the "Year of the Four Emperors", Galba was the one to rise to power during the tumultuous period following Nero's death, hinting at his critical view of Nero's rule.