I created Burp Suite as a side project when I was working as a penetration tester a long time ago. I was basically lazy and wanted to automate my job. I ended up having more fun working on the software than doing actual testing, so I decided to focus on that.
I soon realized that I couldn't do everything I wanted to on my own. Without any real plan, I began assembling a team - the incredible people who have made PortSwigger what it is today. I'm still closely involved in most areas of the business: from hiring, to designing product features, to making sure we stay true to our values. Sadly, I don't get to write code any more, but our products are all the better for that.
It's hard to pick out just one thing. Huge variety, challenge, building cool things, working with exceptional people, getting praise from our customers. Probably overall, because it's so much fun, but the reason it's fun is because of all those other things.
The Coravin. It lets you get wine from a bottle without removing the cork or spoiling what's left. So you can pour a few glasses from several different bottles and come back to the rest weeks or even months later.
Galahad Threepwood from P.G. Wodehouse's novels. He's an energetic bon vivant who is considered disreputable by people whose opinion doesn't matter.