The first chart shows the federal minimum wage going back to 1938, when FDR first signed it into law. Back then, the minimum wage was 25 cents.
In today’s dollars, that would be worth $4.13.
The minimum wage had its highest buying power in 1968, when it was worth about $10.71 in today’s dollars. At $7.25 in 2014, it’s current in between those two extremes.