One of Satoshi's final messages was an email he wrote to Mike Hearn on April 23rd 2011, exactly 10 years ago today: "I’ve moved on to other things. It’s in good hands with Gavin and everyone"
My favorite pet theory was that Satoshi was actually a hyper-intelligent cyber-dolphin from outer space, and he needed to go back home. This was the cartoon I made four years ago to commemorate that moment.