It is interesting that if you read the first chapter of John, you will notice that when John says:
John 1:18
18 No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared him.
From reading this, who do you think is being referred to as God? Who did Jesus declare as God? Was it not the Father?
Who then was it that Moses and the other prophets of old saw? Jesus taught:
John 8:53-59
53 Art thou greater than our father Abraham, which is dead? and the prophets are dead: whom makest thou thyself?
54 Jesus answered, If I honour myself, my honour is nothing: it is my Father that honoureth me; of whom ye say, that he is your God:
55 Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a liar like unto you: but I know him, and keep his saying.
56 Your father Abraham rejoiced to see my day: and he saw it, and was glad.
57 Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham?
58 Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I AM.
59 Then took they up stones to cast at him: but Jesus hid himself, and went out of the temple, going through the midst of them, and so passed by.
Was it not the Great I AM whom the prophets of old saw? Was it not Jesus (aka Jehovah)? John was correct in saying that no man hath seen God (the Father) at any time up to the time He wrote the book of John. It was Jesus whom they saw.
Exodus 3:13-15
13 And Moses said unto God, Behold, when I come unto the children of Israel, and shall say unto them, The God of your fathers hath sent me unto you; and they shall say to me, What is his name? what shall I say unto them?
14 And God said unto Moses, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you.
15 And God said moreover unto Moses, Thus shalt thou say unto the children of Israel, The Lord God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath sent me unto you: this is my name for ever, and this is my memorial unto all generations.
Hosea 13:4
4 Yet I am the Lord thy God from the land of Egypt, and thou shalt know no god but me: for there is no saviour beside me.
Isaiah 45:21
21 Tell ye, and bring them near; yea, let them take counsel together: who hath declared this from ancient time? who hath told it from that time? have not I the Lord? and there is no God else beside me; a just God and a Saviour; there is none beside me.