Yaddle was a Jedi Master of the Old Republic in the years leading up to the Clone Wars. Of the same mysterious species as Jedi Master Yoda, Yaddle shared his species tendency for longevity. Yaddle was almost five hundred years old during the Separatist crisis that eventually led to the Clone Wars and the destruction of the Jedi. During her lengthy tenure with the Jedi Order, Yaddle had ample to acquire the skills, knowledge, and wisdom required of a Jedi Master.
During her five centuries, Yaddle was involved in many aspects of the Jedi Order. She was head of the Jedi Temple Librarian Assembly, and worked with Jedi Knight Ashka Boda to maintain the Temple's vast collection of ancient scrolls, books, and holocrons - both Jedi and Sith. She was also a master of the forbidden technique known as Morichro, which could be used to slow and eventually stop another's metabolic processes, including their breathing and heart rate. Due to this technique's powerful nature, only the most experienced of Jedi were allowed to study it and it was rarely practiced.
When not on Coruscant, Yaddle spent time at the Jedi training center on Kamparas where she continued to instruct young Jedi in the ways of the Force. Like many Jedi Masters, Yaddle eventually took on her own apprentices most notably Empatojayos Brand and Oppo Rancisis. Brand served the Jedi Order during the Clone Wars and barely escaped the Jedi Purge. Going into hiding, Brand would eventually emerge to fight alongside Darth Vader's son, Luke Skywalker, during the galactic threat of his time. Yaddle had the extreme pleasure of seeing her former Padawan, Rancisis, eventually ascend to the rank of Jedi Master himself and join her on the Council.