Before the reveal that his real name was Grogu, "Baby Yoda" captured the hearts of Star Wars fans from the moment he was first introduced in The Mandalorian Disney+ series. In the show, he was initially referred to as The Child or The Asset, but since he was obviously of the same mysterious species as Jedi Master Yoda, fans latched onto that Baby Yoda label. But Grogu is not the only character of the species found in the franchise. Star Wars: The Phantom Menace introduces Yaddle, a female of Yoda's species who also sits on the Jedi Council. She has no speaking lines in the film saga, and is not seen on screen again after The Phantom Menace. Her character was developed from concept art of a young Yoda, long before the idea of Grogu came to be.
Concept artist Iain McCaig was inspired to recreate a story he heard of an eight-year-old Tibetan boy who carried his two-year-old brother 25 miles in order to escape the invading Chinese. He believed that a young Yoda had the possibility to achieve a similar feat of bravery, love and devotion. The concept art was intended to not only show Yoda's youth, but also his commitment to justice, as well as the pain and wisdom that comes from surviving a devastating hardship. Ultimately, the exploration into Yoda's youth was dropped, but the concept art was not wasted. It was then used to inspire the look of Yaddle.
While Yaddle only briefly appears in the Star Wars films, she actually is a significant member of the Jedi Order, according to the non-canon Legends. She has a special ability that is very rare among the Jedi that she acquired through intense study. This power allows her to control the heart rate of an opponent at her own will using her special control of the Force. She gained this knowledge in part because of the time she spends as the head of the Librarian's Assembly of the Jedi Temple.
In Star Wars canon, Yaddle spends much of her time among some of the greatest Jedi scholars. She not only encourages them, but absorbs their teachings. Yaddle also trained Padawans and had several notable apprentices including fellow Council-member Oppo Rancisis and Empatojayos Brand.
However, within the fandom, Yaddle, while wise and skilled, is often mocked for just looking like Yoda in a bad wig. Her origin as a concept for a young Yoda did her no favors in the looks department.
Young Yoda does appear later on in canon, but he doesn't actually look like the concept art that eventually became Yaddle. In Star Wars: The High Republic #1 by Cavan Scott, Ario Anindito, Mark Morales, Annalisa Leoni and VC's Ariana Maher, young Yoda actually appears as a young and capable Jedi Grandmaster. He looks just as he does in the films, if perhaps a little less frail. This seems to imply that there actually isn't that much of a biological change in this mysterious species with age and the key difference between genders is the hair.
Yaddle only briefly appears in the Star Wars film saga, and perhaps her origin has something to do with that fact. She started as a concept drawing for the child version of fan-favorite Yoda. When Yoda's backstory was not explored as intended, the concept art was recontextualized to reflect the female of Yoda's mysterious species instead. But the recontextualization did Yaddle no favors and her character slipped away from the Saga before she really got an opportunity to flourish.