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The Yangwu avatar was discovered by the Southern Air Temple prior to the Air Nomad genocide, but his personal identity had not been revealed to the world at the time of the Air Nomad Genocide. What became of the young Avatar is not known. Most people assume he was killed, or escaped but lived an ordinary life in obscurity with the scattered survivors without having ever been told of his true nature.
Some people who use the Avatar Era for writing dates continue to extend the Yangwu era indefinitely, absent any information about succeeding Avatars. If the Yangwu Avatar is still alive, he must be quite old, about 107 years as of 95 AG.
Artist's conception
See also Aang on the Avatar Fandom wiki, for how the Yangwu Avatar's life played out in the show canon.
Translator's Note
武 has a basic meaning of "military," which is pretty straightforward; 氜 is more complicated. The character (aptly, given its composition of "air" and "sun" radicals) was at one time used for the element helium but is considered to be a variant form of 陽. This is the famous "Yang" of "Yin and Yang" and you can draw your own conclusions about what the basic concept means, as my humble knowledge of the topic of Chinese philosophy does not suffice to explain it here. But notably, 陽 appears in the compound 太陽, "the sun", or perhaps more literally "utmost yang." The yang principle is strongest in the sun, during summer, etc and is associated with the element of fire. Aang's era is one of Fire Nation ascendancy, and therefore I think it appropriate to render it the era of "Solar Military" after the dominance of Fire Nation militarism. the Avatar fandom wiki gives "Superior Military" but I question this translation and it does not appear at the page of the The Art of the Animated Series cited. If anyone knows why this might in fact be a more appropriate translation than the one I have proposed, in context, please let me know.
Of course, the perspective this era name implies suggests that Avatar era names are assigned by someone other than the Avatar or their discoverers - perhaps by Wan Shi Tong or some other spirit, and then determined by humans through divination or other spiritual practices.