There are two thoughts about the "faithful and wise slave," as you know some believe it to be one individual. I know of several groups who have their own "faithful slave."
Years ago, it was thought to be Br. Russell, although contrary to populat opinion, he never claimed such a title, then it became what is today taught by the Society that it refers to the anointed ones.
Most commentaries teach that this "slave" is the Christian congregation, however the word slave is singular and not plural.
I believe the "slave" is a special messenger whether [animate or inanimate] his "fellow slaves" are [his] helpers and the domestics or "household," as the King James renders it are Christians in general.
Thus the Scriptures indicate a chief servant of the truth and his fellow servants, assisting in serving spiritual food to the household of faith [Christians in general]. If neither the "household" or "fellows servants" were mentioned, it might be questionable whether the expression "that servant" referred to one or all faithful servants.
Each one of the household is to prove all things he accepts as spiritual food, whether he gets it from the Bible himself or from That servant of fellows servants.
It is interesting that if "that servant" is unfaithful" he will become the evil servant. There are some who believe Jesus is referring to two groups, "that faithful slave" and "that evil slave." But looking carefully, one sees that it should be rendered "and if that servant should say with evil in his heart, the lord delays."
"People in glass houses, shouldn't throw stones"