Work Hard, Play Hard

He's the most efficient person in your workplace. He thinks of plans that work better than anybody else's and can take down anyone when he's attacked. He might be a harsh employer or a kind helper who teaches you how to make your work habits more efficient. He is always professional and mature, if not a little too uptight. Either way, you can always rely on him for anything, as long as it's work related.

One day, he invites you to hang out with him after work. Curious, you agree.

You're surprised to see him break open the alcohol, start screaming karaoke or show other wild behaviors that you never saw at work. Turns out, he spends as much energy partying as he does working hard. He might even use the fact that he works so hard as an excuse to why he plays so hard.

Truth in Television here, as relaxing and having fun is good way to keep stress levels down. Being social is also a good way to find employment and learn from others, so a complete workaholic is pretty tough to find in Real Life. There's also the fact that most people enjoy having fun and relaxing — but need to work to earn money. Frequently this is the other side to characters like The Reliable One.

Examples of Work Hard, Play Hard include:

Anime and Manga

Misato from Neon Genesis Evangelion
This is pretty much the mindset of all the salarymen in Virgin Love and its related series.

Film

Tony Stark in Iron Man more clearly demonstrated this trope at the beginning of the movie, where he's pretty much inventing state of the art weapons system in between having crazy hardcore parties. He stops playing so hard, though, when his experience in Afghanistan leads him to make very serious efforts to curb the violence.
- I dunno, rousting the terrorists out of Gulmira looked pretty fun to me.
The late Charlie Wilson, as portrayed in Charlie Wilson's War, fell under this. Well, after he decided to get involved in Afghanistan, anyway — we see little evidence of the "work hard" before that.
Lt. Rasczak in Starship Troopers encourages this for his men. "Here's the beer! Here's the entertainment! Now, have fun - that's an order!"

Literature

In the Star Trek Expanded Universe of novels, there was a temporary security chief on the Enterprise who embodied this trope: a total hard-ass with his staff on-duty, but off-duty he parties with them in the lounge, and as a result, their loyalty to him is absolute.
The declared mission statement of Hawkeye, Duke, Trapper John et al in the original MASH novel is to be such brilliant and reliable surgeons when they're on duty that they can get away with absolutely any crazy shit they feel like pulling when they're off duty. It works.
The king in Dr. Seuss's The King's Stilts. The whole theme of the book is why only working is not emotionally healthy and causes problems in the long run.

Live Action TV

Jadzia Dax from Star Trek: Deep Space Nine is an exceptional science officer who enjoys partying hard, gambling with Ferengi, brawling with Klingons, drinking, rough sex, fun on the holosuite, and playing practical jokes, and still finds time to be the station's biggest gossip.
As in the literature example above, the characters from M*A*S*H maintain a healthy level of insanity whenever they are off-duty, as a defense mechanism against the horrors of war.

Western Animation

In The Simpsons, Homer was worried that Bart was turning gay and he brought Bart to a steel mill to show him manly men doing manly jobs. Turned out it was a Manly Gay steel mill. Then the 5 o'clock whistle blew, and the place became an industrial-themed gay dance club. "We work hard, we play hard."
In Young Justice, Word of God says this is the general perception the public has of Bruce Wayne, rather than as the usual Rich Idiot With No Day Job he depicts himself as in other continuities.

Real Life

In Real Life, Germans are said to be like this.
- Also the Japanese, according to some.
  - The phrase "Work hard, Play hard," could very well be the national motto of the United States. On average, most Americans work more hours than their counterparts in other Western nations and take vacations less often, but once work is done for the day or week, the movie theaters, parks, local bars, beaches, sports venues, and other recreational areas flourish with customers. We Americans generally take the attitude that we're proud to accomplish our work, but we also love to party.
Many U.S. university student bodies stake a claim to this concept as a guiding philosophy, complete with the slogan, "First we'll out-think you, then we'll out-drink you."
Elizabeth I was rather like this. She loved giving parties and men made elaborate (and perhaps somewhat suspicious) statements of Courtly Love toward her.
Christopher Titus described his father this way; he never missed a chance to get drunk, high, or laid, but he also never missed a day of work.