The first person to be baptized in the full significance of New Testament baptism was the Lord Jesus Christ himself. He was "baptized" on the cross. The second would have been the thief although it could be argued that he is awaiting the crucial part of the process, resurrection to newness of life; so the thief's baptism is, to date, incomplete. Compare these verses:
But Jesus answered and said, Ye know not what ye ask. Are ye able to drink of the cup that I shall drink of, and to be baptized with the baptism that I am baptized with? They say unto him, We are able. (Matthew 20:22)
And he saith unto them, Ye shall drink indeed of my cup, and be baptized with the baptism that I am baptized with: but to sit on my right hand, and on my left, is not mine to give, but it shall be given to them for whom it is prepared of my Father. (Matthew 20:23)
But I have a baptism to be baptized with; and how am I straitened till it be accomplished! (Luke 12:50)
Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. (Romans 6:3-6)
I hope you have found this helpful.