The earliest Creed is probably "Jesus Christ is Lord". Creedal language became more robust with time, and were very likely an outgrowth of baptismal confessions.
Consider this Baptismal Confession from the Apostolic Traditions attributed to St. Hippolytus of Rome,
"When the elder takes hold of each of them who are to receive baptism, he shall tell each of them to renounce, saying, 'I renounce you Satan, all your service, and all your works." After he has said this, he shall anoint each with the Oil of Exorcism, saying, "Let every evil spirit depart from you." Then, after these things, the bishop passes each of them on nude to the elder who stands at the water. They shall stand in the water naked. A deacon, likewise, will go down with them into the water. When each of them to be baptized has gone down into the water, the one baptizing shall lay hands on each of them, asking, "Do you believe in God the Father Almighty?" And the one being baptized shall answer, "I believe." He shall then baptize each of them once, laying his hand upon each of their heads. Then he shall ask, "Do you believe in Jesus Christ, the Son of God, who was born of the Holy Spirit and the Virgin Mary, who was crucified under Pontius Pilate, and died, and rose on the third day living from the dead, and ascended into heaven, and sat down at the right hand of the Father, the one coming to judge the living and the dead?" When each has answered, "I believe," he shall baptize a second time. Then he shall ask, "Do you believe in the Holy Spirit and the Holy Church and the resurrection of the flesh?" Then each being baptized shall answer, "I believe." And thus let him baptize the third time." - The Apostolic Traditions, 21:9-18
Even earlier, in the writings of Irenaeus we find a similar confession,
"The Church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: [She believes] in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations of God, and the advents, and the birth from a virgin, and the passion, and the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord, and His [future] manifestation from heaven in the glory of the Father "to gather all things in one," [Ephesians 1:10] and to raise up anew all flesh of the whole human race, in order that to Christ Jesus, our Lord, and God, and Saviour, and King, according to the will of the invisible Father, "every knee should bow, of things in heaven, and things in earth, and things under the earth, and that every tongue should confess" [Philippians 2:10-11] to Him, and that He should execute just judgment towards all; that He may send "spiritual wickednesses," [Ephesians 6:12] and the angels who transgressed and became apostates, together with the ungodly, and unrighteous, and wicked, and profane among men, into everlasting fire; but may, in the exercise of His grace, confer immortality on the righteous, and holy, and those who have kept His commandments, and have persevered in His love, some from the beginning [of their Christian course], and others from [the date of] their repentance, and may surround them with everlasting glory." - Against Heresies, Book I, ch. 10:1
The Old Roman Symbol already has been mentioned, but it is representative of this very early creedal tradition.
That we believe in one God the Father, who made all things.
And in one Lord, Jesus Christ, the Son of God.
And in the Holy Spirit.
And in the holy catholic Church.
And in the resurrection of the body.
And in the life everlasting.
This is the Christian faith.
-CryptoLutheran
