The bull that serves as Shiva’s vehicle is Nandi. In Sanskrit, a vehicle or mount of a deity is called a vahana, and Nandi is Shiva’s sacred bull and one of his foremost attendants.
Nandi is usually portrayed as a powerful white bull seated or kneeling before Shiva’s shrine. In many Shiva temples, a Nandi image faces the main sanctum and looks toward the Shiva linga. This arrangement is not merely decorative: it represents Nandi’s constant devotion and his role as a guardian who stands between the worshipper and the deity.
The other options belong to different divine associations. Garuda is the eagle-like vehicle of Vishnu, Airavata is Indra’s legendary elephant, and Makara is a mythical aquatic creature associated with several deities and symbols. Nandi is also called Nandikeshvara or Nandideva, and traditions portray him not only as an animal mount but as a divine gatekeeper, devotee, and teacher connected with Shaiva worship.