First of all, there is only ONE GOSPEL (1 Cor 15:1-4), therefore it is frequently called just "The Gospel", and Christ said (Mk 16:15) "...Go ye into all the world and preach THE GOSPEL to every creature"
At the same time, it has various designations: it is the Gospel of God, the Gospel of the Grace of God, the Gospel of Christ, the Gospel of Your Salvation, and the Gospel of the Kingdom. Those who claim that there are multiple Gospels are not rightly dividing (interpreting) the Word of Truth.
When Christ came at His first coming, He came as the King-Messiah of Israel according to OT prophecies. That's why before His crucifixion He rode into Jerusalem on a donkey, and was hailed as the One who "cometh in the name of the Lord". Therefore, while on earth, He preached "the Gospel of the Kingdom". But at the same time He required faith in Himself as the Son of God for people to be saved.
The Gospel is that Christ died for our sins according to the Scriptures, that He was buried, and that He rose again the third day according to the Scriptures (1 Cor 15:1-4), therefore "repentance and remission of sins shold be preached in His name among all nations" (Lk 24:47). The Gospel also includes the truth that God has made Him both Lord and Christ (Acts 2:36).