Maa Durga
The fierce and protective mother goddess, celebrated during Navratri as the victor over evil.
Who Maa Durga is
Durga is the supreme mother goddess — Shakti, the divine feminine power — invoked in her fierce, protective form when evil has grown too strong for the gods alone to handle. Tradition holds she was created by combining the collective energy (tejas) of all the gods specifically to defeat the buffalo demon Mahishasura, whom none of them could defeat individually.
Iconography
She's depicted with ten (sometimes eight) arms, each holding a weapon gifted by a different god — Shiva's trident, Vishnu's discus, Indra's thunderbolt among them — riding a lion or tiger into battle. This iconography itself carries a message: real protection often requires drawing on many strengths at once, not just one.
Navadurga — her nine forms
During Navratri, nine distinct forms of Durga (Navadurga) are worshipped on nine successive nights, each representing a different quality — courage, wisdom, prosperity among them — building toward Vijayadashami (Dussehra), which celebrates her victory over Mahishasura.
How she's worshipped
Navratri and Durga Puja (especially elaborate in Bengal) are her major festivals, involving fasting, elaborate idol worship, and community celebration. She's approached both as a fierce protector in times of difficulty and as Jagadamba — mother of the universe — in gentler, everyday devotion.