Yoda wasn't the only member of his species in Star Wars; there was also Yaddle, a Jedi from the prequels who disappeared in the later part of the trilogy. Yoda’s species has been a mystery since the diminutive alien first appeared in The Empire Strikes Back, with the character George Lucas joked could be the illicit love child of Kermit the Frog and Miss Piggy. That changed with Star Wars: Episode I - The Phantom Menace, which introduced Yaddle, a female of Yoda’s species.
In reality, Yaddle was a repurposed test puppet for Yoda himself, but in breaking such a hard-fast Star Wars rule, was immediately intriguing. However, despite some character expansion in both the Expanded Universe (now Legends) and wider canon, Yaddle disappeared by Star Wars: Episode II - Attack of the Clones and was never mentioned again.
In the Expanded Universe, Yaddle sacrificed herself while on a mission alongside Jedi Master Obi-Wan Kenobi and his apprentice Anakin Skywalker. They were attempting to end a cycle of violence on the lawless world of Mawan, but were unable to prevent the release of a potent bioweapon; Yaddle absorbed it into herself, dying instantly. In the new Disney canon, however, Yaddle's fate is unknown. She's said to have retired shortly after the Battle of Naboo, but has never been seen again.
In truth, Yaddle is now something of a blank page in Star Wars history. According to the Star Wars Character Encyclopaedia, she was born around 509 years before the Battle of Yavin, and was brought to the Jedi Temple at some point in her life. She had a long and distinguished career as a Jedi Master, serving on the Council alongside at least one of her old Padawans. Yaddle withdrew from active service shortly after Qui-Gon's death, with her seat taken by Shaak Ti.
Yaddle may seem to be something of a deep cut in Star Wars lore, but it's possible she's about to become rather more important. Star Wars' first-ever live-action TV series, The Mandalorian, has introduced a new member of this mysterious race, colloquially known as "Baby Yoda". Interestingly, the infant would have been born just before Star Wars: Episode I - The Phantom Menace, and there's been some speculation the child could be connected to Yaddle in some way.
Meanwhile, Yaddle herself was unexpectedly mentioned in the Jedi: Fallen Order game, which hinted she may have gone into hiding and survived the Emperor's Purge. That seems doubtful, however, given Darth Vader believed she was dead; in Charles Soule's Darth Vader series, the Dark Lord of the Sith experienced visions of Jedi Masters from the past, including Yaddle, and insisted they were all dead. That may well mean that Vader himself was ultimately the one who cut Yaddle down.