Who was on the fourth cross at golgotha?

There was not a fourth cross at golgotha, but only three.

Jesus was on the cross in the middle.

Then were there two thieves crucified with him, one on the right hand, and another on the left. Matt 27,38

According to some early writings, the names of the two crucified with Jesus were Dysmas and Gistas.

His name was Gistas. And he that was crucified on the right, Dysmas by name, reproved that robber, saying: O wretched and miserable man, dost thou not fear God? Apocrypha Gospel Infancy Of Nicodemus 2 10,28