Updated: Apr 18, 2018
The Mongkhon or Mongkol (headband) and Pra Jiad (armbands) are often worn into the ring before the match begins. They originate back in times when Thailand was in a constant state of war, where young men would tear off pieces of a loved one's clothing (often their mother's sarong) and wear it to battle for good luck as well as to ward off harmful spirits. In modern times the Mongkol (lit. meaning holy spirit, luck, and protection) is worn as a tribute to the gym that the Muay Thai fighter is fighting out of. The Mongkol is traditionally presented by a trainer to the fighter once he feels that the fighter is ready to represent the gym's name in the ring. Often after the fighter has finished the Wai Kru, the trainer will take the Mongkol off of his head and place it on their corner of the ring for luck.
Whether the fighter is a Buddhist or not, it is common for them to bring the Mongkol to a Buddhist monk who blesses it with good luck prior to stepping into the ring