This character will fly slowly over your village in his flying machine every once in a while. If you stop him, he will walk to your Workshop and speed up anything you have crafting by 1 hour. If there's anything less than an hour left on what you have crafting, he'll automatically finish the craft. He only appears if there's something crafting in the workshop, but if the item finishes while he's flying in the air and you tap him, he will land, stand there, and fly away again. It's best to quickly begin crafting something else that you have the materials for, as it's better to craft something than to waste a free hour. If he slips on bird poop on the way to the workshop, when he gets back up he will leave without visiting the workshop. He appears to be a form of Hermes, the Greek God of Speed, Travel, and Messages. His name was finally revealed in the 1.3.0 update (Christmas Update). If you've finished all the quests before the update, this is the quest you'll start with.
"There's no time! Here's a book where I've written exactly what is needed so that everything goes well. I can't tell you more."
If the item being crafted in the Workshop completes while Leo is in the process of walking to the Workshop, it is possible to start crafting a new item without Leo turning around and flying off. To accomplish this switch, do not collect the finished item that appears above the Workshop, but instead tap on the Workshop and then the "Craft" button and select a new item. When starting a new craft the one that is ready will be collected automatically. It is also important that a new item is crafted soon after the completion of the prior one or Leo will turn around and fly off; the actual time you have to start a new craft is currently unknown.