Question: why is uldren a guardian?
Answer: We knew that, of course, from a brief cutscene late last year. Now, we know what he's been up to since. After getting shot in the head to avenge the fallen Cayde, Uldren was revived as a Guardian by a cheerful Ghost named Pulled Pork. ... And so Uldren woke up with no record of his heritage, or knowledge of what he's done.