You mean Joesph Smith, and who said he was JW.
D&C 77:
11 Q. "What are we to understand by sealing the one hundred and forty-four thousand, out of all the tribes of Israel—twelve thousand out of every tribe?"
A. "We are to understand that those who are sealed are high priests, ordained unto the holy order of God, to administer the everlasting gospel; for they are they who are ordained out of every nation, kindred, tongue, and people, by the angels to whom is given power over the nations of the earth, to bring as many as will come to the church of the Firstborn."
It looks to me like the 144,000 are going to be LDS missionaries. In the Melchizadech priesthood there are two levels, Elder, which faithful male members of the Church are eligible at the age of 18, along with adult new converts. And then there is the high priest. The age requirement is only that you have to have been an elder for one year, but usually the bishop only calls more mature, very faithful members. To be a bishop or stake president, or hold any higher authority in the Church, you have to be a high priest. Members receive a patriarchal blessing, usually in their youth. This blessing, the same type of blessing that Jacob gave his 12 sons, also declares what lineage in the House of Israel a member is. For example my patriarchal blessing declared my lineage from Ephraim. Most members have been from Ephraim and the tribe of Joseph. A lot of Manasseh also. But since the gospel has grown to many nations, there are likely members from all twelve tribes in the Church. And this will just grow more in the future. The missionary program is gathering scattered Israel into the Church of the First Born. Currently there are about 80,000 full time LDS missionaries, most who are elders and not high priests. It looks like in the future, likely just prior to the Second Coming, there will be 144,000 high priests of The Church of Jesus Christ pf Latter Day Saints, 12,000 from each of the twelve tribes, who will try and share the gospel with the world.