He was incredibly hard working, in the early days of Square he owned the engineering hiring process and was on the interview panel for every engineer up through the company having hundreds of engineers. It was just an amazing amount of work he put into this. When there weren't enough hours in the day, he started delegating, but the whole engineering culture was just incredibly shaped by his hard work.
In spite of being very accomplished as an engineer, he was humble and knew what he didn't know. I worked in infrastructure and Bob was much more of a mobile guy. He deferred to our expertise in the areas where he wasn't an expert.
Some years after we'd both left Square I was interviewing for at various companies. I noticed a shared connection at one company. I asked Bob for any background, and unprompted he sent a glowing recommendation to that company.
And then CashApp. That started as a hack week project led by Bob. It was all email based, I remember how excited he and Jack were about it. It was cool, and IIRC, we actually launched the email only version of it before Square Cash and then CashApp evolved into what it is today.