The one dollar coin denomination (written as $1) was introduced in Australia in 1984, replacing the earlier banknotes. The original reverse design by Stuart Devlin on circulating coins has not been changed since its introduction. The denomination is also often used to issue circulating commemorative coins with various reverses.
The denomination is also used by both the Royal Australian Mint and the Perth Mint to issue an extensive range of collector coins which are legal tender in Australia but are not intended for circulation - such as this one. The coin is larger than the normal $1 coins.
This non-circulating $1 coin was issued in a Stamp and Coin Cover as part of the Perth Mint's Lunar Series III to mark the Chinese Year of the Ox (12 February 2021 - 31 January 2022).
The Mint says about it:
"First issued in 1995 and now in its third round, the long-running Australian Lunar Coin Series celebrates the animals of the Chinese zodiac with a sequence of annual designs portraying the mouse, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog and pig. These 2021 coins celebrate the Year of the Ox, whose rule over every second year in the 12-year lunar cycle is said to influence people born during 1949, 1961, 1973, 1985, 1997, 2009 and 2021.
According to Chinese mythology, the order of the animals in the ancient zodiac calendar was decided with a great race across a river. Traditional storytellers say the magnanimous ox offered to carry the mouse across the water - and thus it was that on the opposite bank the diminutive creature was able to leap from the ox’s head and claim first place!
Legend has it that each zodiac animal influences the personality of the people born under its ‘rule’. Those born in the Year of the Ox are said to possess the same qualities displayed by the kind, hardworking and determined creature who first participated in the fabled event." | 
Search for Australia: One Dollar 2021 Year of the Ox, Perth Mint on eBay 
