JOEL - You know I was just thinking something similar the other day as I was reading a U.S. history year book during the time I was born. Do you know that there is not one mention of me even being born in that book, nor do any of the following year books mention anything I did in my life time? :-)
I guess someone forgot to mention Laban as well in the Bible.
I wouldn't call Laban a "ruler". The only hint we get about Laban's status in Jerusalem is found in 1 Nephi 4:22, where it implies that he might have been one of the prominent elders of Jerusalem, having several servants(1 Nep 3:25).
He may also have been some sort of military leader as well considering that he owned a suit of armor and a rather remarkable sword. (1 Nep. 4:9)
How Laban obtained the brass plates and where they originally came from are not known. Several theories have been advanced, including the possibility that the plates of brass originated in the days of Joseph of Egypt. The Book of Mormon indicates that Laban and his father had inherited and preserved the record because they were descendants of this Joseph (1 Ne. 5:16).
The brass plates contained some of the history and religious doctrines of Lehi's forefathers. It contained copies of scriptures of Isaiah and a couple of other prophets from the Old Testament times. They were important to Lehi because he was about to set out to a new land and wanted to be sure he had a copy of these things to take with him to preserve the knowledge they contained. Laban just happened to have a copy of them.
Just because Laban is not mentioned in the Old Testament does not mean that he didn't exist. He was not a prophet nor a king and evidently not important enough for any other reason to earn a mention.