I am not a bitter person. Sometimes, however, when I look at my Facebook news feed, and see someone posting the hundredth photo of himself with his new girlfriend or new puppy or new Ferrari, I feel a slight wave of revulsion roll over me: one can only take so much happiness. Such was not the case with Benjamin Klein this past February. Every time he posted a wedding photo of himself with his wife, Stephanie Fieger Klein, I thought: They are adorable, and I am genuinely happy for them. 

"We got married on February 12th," Klein told me the other night before showtime, as we sat in the seats of the Beaumont and the crew readied the stage for the performance. "In numerical terms, that's 21212," he added, "to which my wife and I gave all sorts of significance: two become one, and on and on." 

February was significant for Klein for another reason: he officially started his current stint as associate director of "War Horse" that month. "I started learning the show as it was being re-cast, late last year," Klein said. "I was in and out of recasting rehearsals, before taking over officially for Drew Barr in February." 

Klein's main brief is to make sure the production maintains its high level of quality. His day-to-day requirements can be knotty, particularly with regard to the almost Byzantine adjustments that must go into place when someone is out of a performance. (Stage management oversees this process.) "Most 'War Horse' performers," he explained, "do multiple roles each, so when someone is out, there's careful juggling. And if three or four people are out, as has happened occasionally, then the adjustments can get really challenging." 

To ensure preparedness for such contingencies, understudies must be continually at the ready; Klein directs understudy rehearsals once or twice a week. 

After graduating from the University of Michigan, with a BFA in directing, Klein moved eastward. After a professional breaking-in at Hartford Stage, he eventually became part of New York theater's Michigan Mafia, whose two most high-profile members are director Jack O'Brien and director/choreographer Jerry Mitchell. 

"I set 'Hairspray' for Jack in London," Klein said, referring to his work on the core of rehearsals for the West End cast of that musical hit staged by O'Brien and Mitchell. Klein went on to set other companies in the West End, as well companies that have played Canada and around the U.K. "I don't get tired of 'Hairspray,'" Klein confessed. "Every company has an immense energy that you can feed off of." 

Klein, who assisted O'Brien at Lincoln Center Theater in 2006-2007 on Tom Stoppard's magnificent "The Coast of Utopia," first saw "War Horse" in London, at the National Theatre. "There were at least ten times in the show," Klein explained, "that I didn't know how they did what they did." And when he finally found out? "Some things are simpler than I expected. They are done with sound and lighting: they are effects that can only be used this way in live theater." 

If some of the effects are simple, Klein said, the process of performing the show can be complex - and not just in the performance assignments. "The actors go to war eight times a week. I encourage them when they are not performing to get their brains far away from this show. Because it is so intense." 

Brendan Lemon is the American theater critic for the Financial Times and the editor of lemonwade.com.