Gabriel is an Archangel, a type of heavenly angel generally distinguished from ordinary messenger angels. To Christians, he's best known for announcing to the Virgin Mary that she would carry Jesus Christ and give birth to Him, a destiny she openly accepted. To Muslims, he's best known for revealing the Quran to Muhammad, verse by verse.
Veneration towards Gabriel is mostly for safety and protection, as he is also considered a 'guardian angel', one who'd protect faithfuls in their everyday life.
