Breakdown of Актёру стало грустно, потому что ему было некого развлекать.
он
he / it (for a masculine noun) / it (for a neuter noun)
потому что
because
актёр
actor
быть
to be
Questions & Answers about Актёру стало грустно, потому что ему было некого развлекать.
Why do we use ему было некого развлекать instead of у него не было никого развлекать?
The structure некого (or нечего) + infinitive is a special impersonal construction meaning "there is no one/nothing to [verb]." The logical subject—the person who experiences this lack—must be in the Dative case, which is why we use ему. You cannot combine the standard у него нет (he doesn't have) construction directly with an infinitive in this way.
Why is the past tense verb было used before некого?
In the present tense, the pronoun некого means "there is no one" all by itself (e.g., Ему некого развлекать - He has no one to entertain). To put this concept into the past tense ("there was no one"), you must insert the neuter past tense verb было right before the pronoun. For the future tense, you would use будет.
How is некого different from никого? Don't they both mean "no one"?
They do, but their grammar and pronunciation are different! Нéкого always has the stress on the first syllable (нé-) and is used with an infinitive to say "there is no one to [do something]." Никогó has the stress on the last syllable (-гó) and is used in standard negative sentences alongside a negated verb, like Он никого не развлекал (He didn't entertain anyone).
Why is the word for "actor" in the Dative case () at the very beginning of the sentence?