There was a SDE3 in my previous company (a unicorn startup). He could easily go through thousands of lines of code and debug issues. His grasping skill was unreal.
Once our sister org was launching a product and they were stuck on some issue for few weeks. This guy checked their whole code, then checked all the libraries they were using. Eventually he figured out that there was a bug in one of the open-source libraries. Created a wrapper on it, fixed it and shipped the product. All this within 24 hrs.
His low level concepts were so good as well. Like not just writing extensible, concise code and following proper OOPs/design patterns but the internals of how code works. What object would sit where in memory (eden space, survivor space etc.) and how to minimize memory footprint. How threads would interact internally (should we use cyclic barrier or countdown latch).
His communication skill was pretty average but I still learnt a lot from him !!
Awesome, which org ?