A popular belief (at least in Russia) holds that Julius Caesar was good at multitasking; he was able to read, write and give orders simultaneously.
Julius Caesar was the first person praised for his ability to do several tasks simultaneously. He could write, read and give orders at the same time, which made his contemporaries look at him in awe.
–"Truth About Multitasking", via Internet Archive
Like his physical prowess, his mind was robust with practical knowledge, excellent memory and, in today’s lingo, he could multitask with the best. His mental abilities were enhanced by his warmth of spirit. He expressed sincere affection and devotion to his mother, wives and his daughter. His ethics were beyond reproach.
A good example [of multitasking] is a story about Julius Caesar... Plutarch [wrote], “Caesar disciplined himself so far as to be able to dictate letters from on horseback, and to give directions to two who took notes at the same time, or as Oppius says, to more.” Plutarch’s Lives (New York, 1905), IV, p. 274. Pliny wrote, “We are told that [Caesar] used to write or read, and dictate or listen simultaneously, and to dictate to his secretaries four letters at once, on his important affairs—or, if otherwise unoccupied, seven letters at once.” Natural History (Cambridge, 1961), II, p. 565.
This has become a cliche in Russian, so a Russian can say "who does he think I am, Julius Caesar?" when, say, their boss gives them too many jobs to do at once.
Is it backed by any historical evidence?