Albert Barnes Commentary Ezra 4:5

"and hired counsellors against them, to frustrate their purpose, all the days of Cyrus king of Persia, even until the reign of Darius king of Persia." — Ezra 4:5 (ASV)

Hired counselors - Rather, “bribed” officials at the Persian court to interpose delays and create difficulties, in order to hinder the work.

Darius - that is, Darius, the son of Hystaspes.