The Shurangama Mantra is a mantra that appears in the Shurangama Sutra. It is also known as the 'Shurangama Chant', 'Great Shurangama Mantra', and 'Buddha's Crown Shurangama Mantra'. It consists of 2620 characters and is considered the longest mantra in Buddhism, often referred to as the 'King of Mantras'.