The name Michael — Hebrew Mikha'el — is a rhetorical question encoded as a name: "Who is like God?" (from mi, who; ka, like; El, God). The implied answer is: no one. The name is both a declaration of divine supremacy and a challenge — the battle cry of the archangel who confronted Lucifer's claim "I will be like the Most High" with the counter-declaration of God's incomparable nature. Michael's name is his weapon before his sword is drawn.
Michael first appears in the Hebrew Bible in the book of Daniel, where he is described as "the great prince who stands guard over your people" — the celestial protector of Israel. This is his foundational role: the divine warrior who stands between his people and the forces that would destroy them. In Daniel 10, he assists the angel sent to Daniel against the "prince of Persia" (a celestial being governing that empire) — suggesting a complex angelic geopolitics in which different angels govern different nations, and Michael governs Israel.
From this starting point, Michael's role expanded enormously across Jewish, Christian and Islamic traditions. He became the commander of the heavenly armies, the angel who defeated Lucifer in the primordial rebellion, the psychopomp who escorts souls to the afterlife, the weigher of souls at the Last Judgment, and the patron of countless nations, cities, guilds and professions. No other angel has accumulated this breadth of function and this depth of devotion across so many traditions.