Conversation so far:
What was Batman: Earth One?
Batman: Earth One is a series of graphic novels published by DC Comics as part of the Earth One line
What was some things that happened in Batman: Earth one to Alfred Pennyworth?
Alfred lost a leg in an explosion. After Thomas Wayne saved his life following the explosion, he helps create a prosthetic leg to replace the one that Alfred lost

Question: What did he do after leaving the Royal Marines?
Self-contained rewrite: What did Alfred do after leaving the Royal Marines?