Here's the WTS explanation, frankie (not that I agree with it). No other person was ever called "pastor" in the WTS; no one.
w50 7/15 p. 215 Organized Testimony to the New World ***16
Property was purchased at 17 Hicks street, Brooklyn, New York. This came to be known as the Brooklyn Tabernacle. On its second floor was a large auditorium seating 800, and here public addresses by Brother Russell and other Society representatives were to be delivered and other meetings held. The street floor was fitted up for office purposes, and the basement floor for the literature stock and the shipping department. Into this the Society began moving in January of 1909, and on Sunday, January 31, there was an opening celebration, almost 41 years to a day before a similar event this year which we are about to describe.
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The total number attending that Tabernacle opening was about 350 from New York, Brooklyn, Jersey City, Newark, and other cities as far away as Boston. The following Sunday all the friends present from New York, Brooklyn and Jersey City voted unanimously to be parts of a congregation whose home would be at Brooklyn Tabernacle, and they unanimously elected Brother C. T. Russell to be "pastor" of the same. And so the designation "Pastor Russell", by which he became known world-wide, was not because of any self-assumed title. Ephesians 4:11, 12 declared that Christ Jesus would give some of his consecrated followers to be "pastors"; and in view of the pastoral work Brother Russell was doing under the Chief Shepherd Christ Jesus the congregations throughout the earth voted him to be their acknowledged pastor.
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yb75 pp. 36-37 United States of America (Part One) ***At the age of twenty-five, in 1877, Russell began selling out his business interests and went into full-time preaching activity. He then was traveling from city to city delivering Bible discourses at public gatherings, on the streets and in Protestant churches. Because of this work, he became known as "Pastor" Russell. He determined to invest his fortune in the promulgation of the work, devote his life to the cause, prohibit collections at all meetings and depend on unsolicited contributions to continue the work after his own money was exhausted.
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w96 1/15 p. 15 Jehovah?s Sheep Need Tender Care ***One of these men was Charles T. Russell, the Watch Tower Society?s first president. He was called Pastor Russell because of his loving and compassionate activities in shepherding the flock under the Chief Shepherd, Jesus Christ. Today, Christian elders are appointed by the Governing Body of Jehovah?s Witnesses, and care is exercised not to use such terms as "pastor," "elder," or "teacher" as titles. (Matthew 23:8-12) Yet, present-day elders do a pastoral, or shepherding, work for the benefit of the sheep of Jehovah?s pasturage.