Past
Your past is all of the experiences your character has gone through before ending up where they are now. Roll 3x 1D20 in order to get a what, a who/where, and a how, write them down on your character sheet, and jot down the bonuses they bring to your character in their respective fields.
You may interpret your past any way you like, and the GM is free to use your past as truths, build their story around it, or use them for future encounters. The past is a great starting point to build a background for your character. Look up the locations and beings in your past and expand upon the events. What dead god was it? Where in Babylon did this happen? Was someone with you? What happened before or after this event, and are there any repercussions that affect your current situation? There is a ton of information in this book, and you can expand your research to other sources. Astro Inferno is a game about creating your own dark legends, and the past is the first step.