https://www.jwfacts.com/watchtower/faithful-discreet-slave-changes.php
Timeline of who was the faithful and wise servant: Is it apparent that the faithful slave is the Governing Body? No, as shown by Watchtower changing its understanding of the parable several times.
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Originally, Russell said the Slave was an illustration of the entire body of Christ, the little flock of 144,000 heavenly rulers.
""Who then is that faithful and wise servant whom his Lord hath made ruler over his household," to give them meat in due season? Is it not that "little flock" of consecrated servants who are faithfully carrying out their consecration vows - the body of Christ - and is not the whole body individually and collectively, giving the meat in due season to the household of faith - the great company of believers?" Zion's Watch Tower 1881 Oct/Nov p.5
Later, the slave was used to refer to a single person, Pastor Russell. (This interpretation was originally suggested by Russell's wife in a letter dated 1895. See Zion's Watch Tower 1906 Jul 15 pp.215-216 for a reprint of the letter.) Russell was thought to have been appointed as the Slave to direct the domestics (Jesus true followers) immediately prior to the Second Coming. Zion's Watch Tower 1896 Mar 1 pp.47,48
"Thousands of the readers of Pastor Russell's writings believe that he filled the office of "that faithful and wise servant," and that his great work was giving to the Household of Faith meat in due season. His modesty and humility precluded him from openly claiming this title, but he admitted as much in private conversation." Watch Tower 1916 Dec 1 p.356
Russell continued to be considered the Faithful Slave after his death in 1916.
"THE WATCH TOWER unhesitatingly proclaims Brother Russell as "that faithful and wise servant." He delivered the message faithfully, finished his course and has now entered into his reward. Through him the Lord gave to the church the message that is so essential to each one who in this harvest time would win the glorious prize." Watch Tower 1917 Mar 1 p.67
"We believe that all who are now rejoicing in present truth will concede that Brother Russell faithfully filled the office of special servant of tile Lord; and that he was made ruler over all the Lord’s goods." Watch Tower 1923 Mar 1 p.68
With Russell's death, a new interpretation became necessary. In the 1917 leaflet The Parable of the Penny, Rutherford was described as the Steward, replacing Russell.