Who is the author of the Plan of Salvation and who presented it at the grand council in Heaven?
Heavenly Father is the creator of the Plan of Salvation. Elder L. Tom Perry explained this simply in the October 2006 General Conference when he said
“Our Eternal Father did not send us to earth on an aimless, meaningless journey. He provided for us a plan to follow. He is the author of that plan.”
God created this plan in order to ensure our eternal happiness and help us in our eternal progression. According to Moses 1:39 God has a specific purpose in all he does:
“For behold, this is my work and my glory—to bring to pass the immortality and eternal life of man.”
God’s purpose and will is for us to become like him, and he created this plan so that through Jesus Christ, we can receive all that he has. Paul talks about this in Romans 8:16-17 where he states who we are, and what blessings we could receive if we follow the plan of salvation:
16 The Spirit itself beareth witness with our spirit, that we are the children of God:
17 And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.
Now, as to the second part of your question. We can’t say with 100% certainty who all spoke in the divine council where God presented his plan for us, but we do know God himself presented the plan to us. President (then Elder) Russell M. Nelson spoke about the council in heaven in his April 2000 talk on the Creation. He said:
“A council in heaven was once convened in which we participated. There our Heavenly Father announced His divine plan.”
This makes sense, as he created the plan, and then described it in detail to us. This also fits with the scriptural account we have received concerning the discussion that occurred on who would be our Savior. In Moses 4:1-2, God tells Moses what occurred right after he finished telling us about the plan. He says:
1 And I, the Lord God, spake unto Moses, saying: That Satan, whom thou hast commanded in the name of mine Only Begotten, is the same which was from the beginning, and he came before me, saying—Behold, here am I, send me, I will be thy son, and I will redeem all mankind, that one soul shall not be lost, and surely I will do it; wherefore give me thine honor.
2 But, behold, my Beloved Son, which was my Beloved and Chosen from the beginning, said unto me—Father, thy will be done, and the glory be thine forever.
From this scripture, you can see that this discussion occurred after God had presented the Plan of Salvation to us, and the need for a Savior was explained.