"No one" means no man had seen the Father. When it is left in context of the time and place in which John the Immerser, a man, gave testimony of Yeshua (Jesus) who was "in the world" (vs. 10) manifested as a man, then the definition is restricted to no one of this world. "In the world" gives the place... the world of men. John the Immerser spoke to the priests and Levites who were sent out to ask who John was...men asking of a man.
John 1:18 is translated as "No man hath seen God..." in the ASV, the GNV, as well as the KJV, the AKJV, and a few others.
It is not speaking of the messengers (angels) that are in heaven, only of men that are in the world.
The time was while John was immersing (baptizing) at the river, before Jesus had come to be immersed....before Jesus' crucifixion, and before Jesus' ascension.
As Jesus was the first to rise from the dead, the first fruit of the resurrection (Acts 26:23; 1 Cor. 15:20), then no man had ascended to the Father before Jesus had. So no man had seen God before Jesus was crucified and before He had ascended in Acts 1:9.
When we put everything in context, in the proper time and place, the implications are very revealing. As no man (no one) had ascended to the Father before Yeshua, then the so-called Book of Enoch is a lie!
Further discussion of these points is available at my blog ShreddingTheVeil, specifically the posts "Frequent Mistakes - Part VII: The Translation of Enoch and Elijah" here, as well as "The Book of Enoch: Fable or True" here, "Nephilim - Fallen Ones?" here, and "Nephilim...Reprise: And The Sons of God" here.