In Jerusalem around 600BC, who was Laban? The Book of Mormon speaks of an influential person in Jerusalem named Laban who was the keeper of the record of the Jews, and had power to command at least 50 men (see 1 Nephi 3:31). 


  "Laban hath the record of the Jews and also a genealogy of my
  forefathers, and they are engraven upon plates of brass." (1 Nephi 3:1-27)


We know Laban was a man of some degree of power and influence in Jerusalem, that he had servants, and a treasury, and kept the genealogy of the Jews in his treasury, but it apparently wasn't beneath him to go out and get black-out drunk in the streets (see 1 Nephi 4:7-8). 

Who was Laban? What position did he hold in Jewish society?
Dr. Hugh Nibley, an LDS scholar who did extensive research on the Book of Mormon, discussed this issue in chapter 4 of his book "Lehi In The Desert", describing how Laban fits a quite well-defined role in the culture of his time and place: that of the local military governor.


  But what were the records doing at Laban's house, and who was Laban anyway? 
  
  ...
  
  For ages the cities of Palestine and Syria had been more or less under the rule of military governors, of native blood but, in theory at least, answerable to Egypt. "These commandants (called rabis in the Amarna letters) were subordinate to the city-princes (chazan), who commonly address them as 'Brother' or 'Father.' " They were by and large a sordid lot of careerists whose authority depended on constant deception and intrigue, though they regarded their offices as hereditary and sometimes styled themselves kings. 
  ... The Lachish letters show that such men were still the lords of creation in Lehi's day—the commanders of the towns around Jerusalem were still acting in closest cooperation with Egypt in military matters, depending on the prestige of Egypt to bolster their corrupt power, and still behaving as groveling and unscrupulous timeservers. 
  
  ...
  
  One of the main functions of any governor in the East has always been to hear petitions, and the established practice has ever been to rob the petitioners (or anyone else) wherever possible. The Eloquent Peasant story of fifteen centuries before Lehi and the innumerable Tales of the Qadis of fifteen centuries after him are all part of the same picture, and Laban fits into that picture as if it were drawn to set off his portrait. 
  
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  A few deft and telling touches resurrect the pompous Laban with photographic perfection. We learn in passing that he commanded a garrison of fifty, that he met in full ceremonial armor with "the elders of the Jews" (1 Nephi 4:22) for secret consultations by night, that he had control of a treasury, that he was of the old aristocracy, being a distant relative to Lehi himself, that he probably held his job because of his ancestors, since he hardly received it by merit, that his house was the storing place of very old records, that he was a large man, short-tempered, crafty, and dangerous, and to the bargain cruel, greedy, unscrupulous, weak, and given to drink. All of which makes him a Rabu to the life, the very model of an Oriental pasha. 
  
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  As to the garrison of fifty, it seems pitifully small for a great city. It would have been just as easy for the author of 1 Nephi to have said "fifty thousand," and made it really impressive. Yet even the older brothers, though they wish to emphasize Laban's great power, mention only fifty (1 Nephi 3:31), and it is Nephi in answering them who says that the Lord is "mightier than Laban and his fifty," and adds, "or even than his tens of thousands" (1 Nephi 4:1). As a high military commander Laban would have his tens of thousands in the field, but such an array is of no concern to Laman and Lemuel: it is the "fifty" they must look out for, the regular, permanent garrison of Jerusalem. The number fifty suits perfectly with the Amarna picture where the military forces are always so surprisingly small and a garrison of thirty to eighty men is thought adequate even for big cities. It is strikingly vindicated in a letter of Nebuchadnezzar, Lehi's contemporary, wherein the great king orders: "As to the fifties who were under your orders, those gone to the rear, or fugitives return them to the ranks." Commenting on this, Offord says, "In these days it is interesting to note the indication here, that in the Babylonian army a platoon contained fifty men;" also, we might add, that it was called a "fifty,"—hence, "Laban and his fifty" (1 Nephi 4:1). 
  
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  Returning by night in a third attempt to get the records, Nephi stumbled upon the prostrate form of Laban, lying dead drunk in the deserted street (1 Nephi 4:7). The commander had been (so his servant later told Nephi) in conference with "the elders of the Jews . . . out by night among them" (1 Nephi 4:22), and was wearing his full dress armor. What a world of inference in this! We sense the gravity of the situation in Jerusalem which "the elders" are still trying to conceal; we hear the suppressed excitement of Zoram's urgent talk as he and Nephi hasten through the streets to the city gates (1 Nephi 4:27), and from Zoram's willingness to change sides and leave the city we can be sure that he, as Laban's secretary, knew how badly things were going. From the Lachish letters it is clear that informed parties in Jerusalem were quite aware of the critical state of things at Jerusalem, even while the sarim, "the elders," were working with all their might to suppress every sign of criticism and disaffection. How could they take counsel to provide for the defense of the city and their own interests without exciting alarm or giving rise to general rumors and misgivings? By holding their meetings in secret, of course, such midnight sessions of civil and military leaders as Laban had just been attending. 


There's more (quite a bit more) and the chapter is well worth reading in its entirety if you're interested in the cultural details that Nephi's account left out, but these are the most relevant points.