Uggs have been around for a long time in Australia and New Zealand. There’s actually a long running dispute on whether they originate from New Zealand or Australia. Either way, the first recorded instance of Uggs being manufactured was in 1933. And yes, the name Uggs comes because the inventor’s wife thought the first pair was ugly.
In the 1960s, surfers started using the boots to keep their feet warm when they left the ocean. Soon after, movie theaters in Sydney banned people wearing ripped jeans and Uggs, which made them even more popular amongst rebellious youth.
Those two phenomena helped the popularity of Uggs explode outside Oceania, starting with surfers in California and the rest of the world after.