Gauri is one of the names of goddess Parvati, the consort of Lord Shiva and the mother of Lord Ganesh. Once upon a time, Mother Gauri took bath. As per the practice in Indian households, Ma Gauri applied turmeric on her body during the bath. Then she collected the turmeric paste from her body and made a doll out of it and breathed life. A charming little lad emerged who was posted as the guardian in her palace entrance.
Lord Shiva was denied entry into mother Parvati’s palace by the boy. Shiva was enraged and cut out the head of the boy with his Trishul (trident). Mother Parvati explained to Lord Shiva how she created the boy and felt bad at the boy’s death. In order to make her happy, Lord Shiva asked for an elephant head, placed it on the boy’s body, and gave him life. This is the origin of Lord Ganesh. Upon giving him new life, Lord Shiva posted him as the Lord of his armies. This day of resurrection came to be celebrated as Ganesh Chaturthi. Since it was Mother Parvati (Gauri) who gave birth to Ganesh, Gauri puja became an integral part of Ganesh Chaturthi puja. This is also the reason why the image of Gauri is made in turmeric paste.