First on the long thread (which I'd share a few of it for discussion purposes) before he joined Bitcoin he built protocols like the Opus Codec adopted by streaming platforms like YouTube and Spotify. I went further to check more details on this and found a pdf and article of his where he confirmed building Opus Codec
Second, Greg was a developer but weren't building on the Blockchain until 2011 when he discovered Bitcoin, and didn't consider decentralized consensus on a P2P network realistic. But later began to code and was noticed, in 2012, by a Bitcoin lead developer and promoted to be among the five core developers.
Third, Greg found privacy to be an essential property of every monetary and payment system, hence he encouraged other developers to hold tight of privacy. Hence, to strengthen the network's privacy without any modifications Greg, 2013, built a scheme called counjoins to make transactions more difficult to trace.
Alongside other beneficial contributions he's made in the Bitcoin network, in 2015, was handed a role of BIP editor, and his respect attracted the interest of other developers and they too ideas to Greg first. He always played the role of a teacher, and a lot of us here have read and learnt from his contributions in matters regarding the forum.
Last on this thread (mine) in same year Greg and Adam Back, found a company called blockstream that focus on developing Bitcoin and hiring core developers. All other details regarding why Greg is a btc legend is in the link below. It'll be great to recall that we'll not only participate in Bitcoin by investing money, they're other ways of adding value to the ecosystem just like Greg did when he found Bitcoin. Even non programmers through research and writing can as well pinpoint a means of doing a memorable contribution to Bitcoin.
https://x.com/pete_rizzo_/status/1878079505052413965