Translation:I had directed him many times in the theater.
That's a good point SMAGringo. We are often hit with redundant pronouns, but in this sentence where DL seems to want a specific subject and object there are none. Granted, 99% of the time we would know through context, but when there is none the pronouns are necessary when the answer requires specificity. I'm wondering where the placement of "a él" would be if the object gender was to be specified. Perhaps: "[Yo] lo había dirigido [a él] muchas veces en el teatro."
"Perhaps: "[Yo] lo había dirigido [a él] muchas veces en el teatro."" That is likely correct, but I think the "a él" may be redundant because gender is indicated by the lo. I know there is controversy over the lo/le usage, but at the very least I think the "Yo" is necessary to clarify the "había"
I dunno, given the context of the theater, translating dirigir as "directed" seems like the definitely-correct choice. You don't usually "lead" something in the theater... Or rather, you could, but you'd be talking about playing the lead role. There's a verb in Spanish "encabezar" which can be "to lead, to head up," which might work here? Or you could use "ser el primo" (related to the Italian-ism "prima donna", the leading lady of a production).
"Lo" and "la" are gender specific third person direct object pronouns.
"Le" is a non-gender specific third person indirect object pronoun.
Since the object in this sentence is "him", the pronoun must be "lo" or "le", we just need to determine if "him" is a direct object or an indirect.
There are a few occasions when it may not appear to be the case, but Spanish follows the English rule of direct versus indirect objects: A direct object is whom / what the verb is directly acting upon; An indirect object is whom / what the verb is indirectly acting upon, either explicitly or implicitly through the direct object.
In this sentence "Lo había dirigido / I had directed him" the "him" is the direct recipient of action from the verb, so it is a direct object and the direct object pronoun must be "lo".
Compare "Le había dado la pelota / I had given him the ball." In this sentence the direct recipient of action from the verb is the ball. I had given what? I had given the ball. "Him" is the indirect recipient. I had given the ball to whom? I had given the ball to him. So the indirect object pronoun "le" is used for him, and there is no direct object pronoun as the direct object is stated: la pelota.
If the direct object isn't stated then a direct object pronoun would be needed. Since the "it" in this case would be standing in for "the ball / la pelota" it would need to be "la". To confuse things a tad, the "le" for the indirect object pronoun would need to be changed to "se" because Spanish doesn't like the sound of "le la/lo" so you'd get "Se la había dado - I had given it to him - I had given him it."