The Zodiac Master's real name is Woo Yin. His main goal is clear: Get four Powerbands and revive the Emperor Of The Darkest Yin. He mainly goes after the Snake Power Band, since he feels it should be his. He has a pet snake called King Cobra and uses it as a spy or to help him in fights.
When empowering a stolen Powerband he would normally say “Empower the Darkest Yin” followed by the band he stole, like if he stole the Snake Power band he would say "Empower the Darkest Yin, Snake". He is always a great threat to every Guardian, but Ang, the Golden Dragon, often saves the day. Despite supposedly being very powerful, he is often easily defeated even in situations in which he has the clear advantage (such as having three Powerbands to Ang only using his Dragon Powerband).
He was born in the year of the Snake and attended Master Chin's training classes, and was an exceptional student. When it was time to select a new Snake Temple Guardian, he thought it was going to be his. Ultimately, the Snake Powerband selected someone different (Cobra), which made him feel betrayed by Master Chin and he chose evil as a result, much like the conflict between Ang and Ling. His dream is to get all the Power bands of the Chinese Zodiac, making him invincible.
However, he also has another goal: resurrect the Emperor with four Power Bands.