This has to be one of the best features in XCOM 2 compared to previous instalments. No longer are characters tied to specific playthroughs; you can now export custom characters to the character pool, thereby allowing them to reappear in future campaigns as VIPs or random recruits. I cannot exaggerate the satisfaction of bumping into a former soldier on the battlefield, adding him/her to your new squad, reacquainting yourself with their biographical information and all the things you forgot about them. Sometimes you forget these characters ever even existed, and then they are, back on your team. After several playthroughs, and potentially hundreds of custom characters, the game starts to become entirely populated by your own creations. It's incredibly fun, and something more people should take advantage of.