Names

I must say it's not only the seven deadly sins; the name of almost character in the Fullmetal Alchemist was carefully conceived.

For example, Colonel Roy Mustang is the name of that famous P-51 American fighter in the World War II. As his main supporters, Riza Hawkeye is the eternal early warning aircraft (first introduced in 1964, and is still in service with its turboprop engine!), Jean Havoc is the Russian Mi-28 attack helicopter, and, Maes Hughes is the H-4 Hercules heavy transport aircraft.

And, Dr. von Hohenheim - the father of the Elric brothers - is the German physician during the Renaissance  period (who is usually known as Paracelsus nowadays), who first proposed that many diseases are caused by disturbance of body mineral content.

Alas, of course, there is Madam Dante - the root of all evil.

PS. To me, Maes Hughes is the most adorable character of the entire series, and I can always remember what Colonel Mustang said in the funeral of his faithful friend:

"Killed in Action, and promoted two ranks for it. Brigadier General Hughes. You're the guy who was going to work below me and push me to the top. Then you get yourself killed and pass me in the ranks. I don't know what's more absurd - you or the State."