Origins of modern Daylight Saving Time
Founding father and kite enthusiast Ben Franklin is commonly credited with DST's invention, but this isn't entirely accurate. During his time as envoy to France, Franklin did publish an anonymous letter in which he presented the concept of rising earlier in the morning to take full advantage of the sunlight (and save on candle wax). That said, Franklin's letter is largely understood to be a satire -- he also suggested taxing window shutters and firing off cannons at sunrise -- and he never publicly pursued the idea beyond this publication. He did invent the Glass Armonica, though.
These days, DST is commonly attributed to one of two men (depending on who you ask): a New Zealander named George Hudson, or an Englishman named William Willett, both of whom proposed the daylight-saving idea independently around the turn of the 19th century.
It wasn't until the onset of World War I that DST was officially adopted on the national level, however -- first by the German Empire and Austria-Hungary, who called it "war time," and then shortly thereafter by the British, who gave it the more pleasant-sounding name of "summer time." Both sides had good reason to implement this time shift: in a period as rife with turmoil as WWI, optimizing usage of coal resources and daylight hours was key. The shift was generally repealed once the war ended, but got fired up again once WWII started up, implemented year-round in some countries (like the USA) and summer-only in others.