Who was Abihu in the Bible

Abihu was the second son of Aaron who along with his brother, Nadab, were priests of Israel.

Now Aaron’s sons, Nadab and Abihu, each took his censer, put fire in it, and laid incense on it; and they offered unholy fire before the LORD, such as he had not commanded them. LEVITICUS 10:1 NRSV

God holds spiritual leaders to a strict standard. This principal was illustrated by Abihu, the second son of Aaron, who served as a priest for the Hebrew people (Exodus 6:23). Abihu’s position meant that he had great responsibilities as he represented the people and the sacrifices they offered God. His priestly clothes set him apart from the masses and emphasized his special role in the community. The people likely gave him their rapt attention when he offered them priestly instruction. They respected his work in the tabernacle as he took great care with the holy articles located there.
However, being a popular religious leader or respected member of the ministry did not give Abihu a free pass when it came to revering God.
Early in the wilderness experience of the people of Israel, Abihu and his older brother, Nadab, became reckless in the offerings they brought to God. Rather than take the best care in preparing their sacrifice, they carelessly created an incense offering from common fire rather than from the holy fire source that God had ordained (see Leviticus 10:1–2). God’s judgment on their irreverence came with speed and severity; fire consumed both brothers even as they were in the midst of their insolent act.
God’s immediate reprimand came through Moses when He reminded Aaron and the people: “By those who come near Me I will be treated as holy, and before all the people I will be honored” (Leviticus 10:3 NASB).
God expects every person to treat Him and His instructions with utmost reverence and respect. No pulpit is too big, no ministry is too important, and no position is too prestigious to be exempted from this requirement.