Red Nandi Bull of Shiva 18.01.613
Each Hindu god has their own vahana (the Sanskrit root word for the English term of Wagon) that they use in war or in peacetime. These vehicles typically tend to be endangered species such as eagle, peacock, swan, tiger, owl, or lion. The animals also stand for specific qualities that are consistent with the deity's image & functions.
The Nandi (bull), it is the vahana of Shiva - the god of skies & destruction. Shiva with Nandi is one of the oldest forms of Hindu representation. Nandi signifies strength, load-bearing capacity, and virility. Given that Shiva didn't have to fight fierce battles or travel quickly between the worlds (he spent most time meditating) he didn't have to choose for a more agile vahana similar to Vishnu's. Given that bulls were the main form of transportation in rural India, it made perfect sense for Shiva - who is the most down to earth & connected with rural India - to take a form that was close to the people.
