Most of the time I hear from some Christian friends that the "Father" name for to The LORD was founded by Jesus.
Because I find it odd (if Jesus was the first person to start calling The LORD "Father"), so I looked into the Old Testament and found that there are several verses which call The LORD "Father".
I would like to know whether this form of address (for example maybe in a prayer) was commonly used during Jesus' time (or at least a few years before Jesus was born).
To be honest, I want to make a conclusion that if it was already common during Jesus' time - then I think Jesus was just following the tradition of calling The LORD "Father". Not as the Trinitarians think that Jesus is praying to the First Person of The Trinitarian Godhead, not to himself (as the Trinitarians say that Jesus is the 2nd Person), not to the Holy Spirit (as the Trinitarians say that The Holy Spirit is the 3rd Person).