Besides Henry the Navigator what are some other "second sons" who have made a major historical impact despite not being kings or fighting a civil war to claim the throne?

by [deleted]
Searocksandtrees

This post has been removed; it is an example of a "throughout history" trivia-type question, which is not permitted per subreddit rules. Do feel welcome to resubmit if you are interested in a specific region/culture and time period. Otherwise, this question may be more appropriate for /r/AskHistory or /r/History.