Hawkeyeted, the random draw is one more element in keeping the game enjoyable and not mathematically predictable. You never know whether your randomly acquired leader will be a wuss or a decisive element in a scenario's play. WARNING when storing games in this series, never combine leaders from different games. (Or heck, why not
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Also as a newbie I recommend you buy at least one of the two Campaigns and Commanders books. They allow you to have role-playing leaders (your leaders earn skills which produce die mods in certain tasks). They are on sale now and will not be reprinted because of a change in print-buying at Avalanche. You can also purchase the two cheaply as digital downloads if you wish.