Kayla Itsines is an Australian personal trainer, author and entrepreneur. In her early days, she worked in a gym in Adelaide. She designed aerobic routines for her clients that became very popular. She also lectured students on nutrition and posted before and after photos of her students on Instagram. Within a couple of months, she had hundreds of thousands of followers and people approached her for nutrition and fitness advice. This led to the creation of her Bikini Body Guides, a popular series of eBooks.