Who is Equality 7-2521, and what is his sin?

Equality 7-2521 is man who has always been too curious and too intelligent for his peers and his society, he finds a secret tunnel where he conducts scientific experiments and rediscovers electricity. He tries to show the World Council of Scholars his electrical invention, but he is forced to run away from the City and is joined by Liberty 5-3000, whom he loves and who calls him "the Unconquered." In the process, he realizes the dangers of collectivism and, upon learning the word "I," renames himself "Prometheus."

He explains that the act of keeping a secret journal without the permission of the Council of Vocations is against the law and a sin because his thoughts are not shared, but personal. However, he has committed an even greater crime. He is writing alone in a tunnel with a stolen candle, although the laws require that no one can ever be alone

"It is a sin to write this. It is a sin to think words no others think and to put them down upon a paper no others are to see. It is base and evil. It is as if we were speaking alone to no ears but our own. And we know well that there is no transgression blacker than to do or think alone."