Final answer:
Muammar Gaddafi was the Arab leader responsible for tens of thousands of deaths while trying to remain in power during the Arab Spring in Libya.
Step-by-step explanation:
The Arab leader responsible for the deaths of tens of thousands of people in an attempt to remain in power was Muammar Gaddafi. Gaddafi ruled Libya with an iron fist for 42 years until the Arab Spring movement led to his overthrow.
The uprising in Libya during the Arab Spring was particularly violent and led to the death of thousands, with the exact number still uncertain. It is also noteworthy that Bashar al-Assad of Syria has been responsible for a high number of casualties in the ongoing conflict there; however, Gaddafi's regime was brought to an end during the Arab Spring.