Who is the "Master of Dreams" in Agnon and Judaism?

Greetings all,

I’m currently reading the novel Only Yesterday by Israeli writer Shmuel Yosef Agnon, who was an Orthodox Jew and whose works and style were heavily influence by Judaism and the language of the Bible.

Throughout Agnon’s works, when a character has a dream, he describes the “Master of Dreams” as causing or bringing dreams.

Here’s a line featuring the term from another Agnon novel, A Guest for the Night:

“Before I went to sleep I knew that I would not get through the night without dreaming. And so it was. I myself opened the door to the Master of Dreams, that he might come and provoke me. But I overcame him, and left him behind — and I arose and embarked on a ship full of Jews, old men and old women, lads and maidens. Never in my life have I seen such beautiful people […]”

My question: What is the origin of this concept of the “Master of Dreams” and who is he?

I understand it’s likely from Judaism, but I haven’t found a clear explanation of it. Any insights would be greatly appreciated. Thanks!