One of the Infantes of Carrion, the sons of Count Don Gonzalo, who married the daughters of the Cid. Diego Gonzalez was a grandson and nephew of the Counts of Carrion (the brothers had no historical basis for being called Infantes or Princes).
Historically he was a members of King Alfonso’s royal school. There is no historical record of Diego’s marriage to a daughter of the Cid.
Now the Infantes of Carrion were there, Diego Gonzalez and Ferrando Gonzalez, the sons of Count Don Gonzalo.
When the Infantes of Carrion, Diego Gonzalez and Ferrando Gonzalez, saw the noble present which the Cid had sent unto the King, and heard how his riches and power daily increased, and thought what his wealth must needs be when he had given those horses out of the fifth of one battle, and moreover that he was Lord of Valencia: they spake one with the other, and agreed, that if the Cid would give them his daughters to wife, they should be well married, and become rich and honourable.
Diego and Ferrando, the Infantes of Carrion, have said unto me that they would fain wed with his daughters, if it seemeth good to him; and methinks this would be a good marriage.
And Alvar Fanez arose and took the damsels one in each hand, and delivered them to the Infantes, saying, Diego Gonzalez, and Ferrando Gonzalez, I deliver unto you these damsels, the daughters of the Cid Campeador, by command of King Don Alfonso my Lord, even as he commanded.
When this was done, the Cid went and seated himself on the estrado with the ladies, he and Dona Ximena in the middle, and beside him he placed Dona Elvira his eldest daughter, and by her, her spouse the Infante Diego Gonzalez; and Dona Sol was seated on the other side, by her mother, and the Infante Ferrando by her.
And Diego Gonzalez, the other, ran to a postern door, crying, I shall never see Carrion again! This door opened upon a court yard where there was a wine press, and he jumped out, and by reason of the great height could not keep on his feet, but fell among the lees and defiled himself therewith.
After some time Ferrando Gonzalez crept from under the seat where he had hidden himself, and he came out with a pale face, not having yet lost his fear, and his brother Diego got from among the lees: and when they who were present saw them in this plight you never saw such sport as they made; but my Cid forbade their laughter.
And Diego went out to wash himself and change his garments, and he sent to call his brother forth, and they took counsel together in secret, and said to each other, Lo now, what great dishonour this Ruydiez our father-in-law hath done us, for he let this lion loose for the nonce, to put us to shame.
Now it came to pass in this battle that the Infante Diego Gonzalez encountered a Moor of Africa who was of great stature and full valiant withal, and this Moor came fiercely against him; and when the Infante saw how fiercely he was coming, he turned his back and fled.
No one be this but Felez Munoz the nephew of the Cid, who was a squire; he set himself against the Moor with his lance under his arm, and gave him such a thrust in the breast, that the streamer of the lance came out all red with blood between his shoulders, and he down'd with the dead man and took his horse by the bridle, and began to call the Infante Diego Gonzalez.
And Felez Munoz said, Take this horse, cousin Diego Gonzalez, and say that you killed the Moor; nobody shall ever know otherwise from me, unless you give just cause.
When Felez Munoz saw the Cid, he said, Sir, your son-in-law Don Diego Gonzalez hath great desire to serve and help you in this day's work, and he hath just slain a Moor from whom he hath won this horse: and this pleased the Cid much, for he weened that it was true.
And the women said, Don Diego and Don Ferrando, ye have strong swords and of sharp edge; the one is called Colada and the other Tizona; cut off our heads and we shall become martyrs! But set not this evil example upon us, for whatever shame ye do unto us shall be to your own dishonour.
And he turned towards the Infantes of Carrion, and said, Ferrando Gonzalez and Diego Gonzalez, I say that ye are false traitors for leaving your wives as ye left them in the Oak-forest; and here before the King I attaint you as false traitors, and defy you, and will produce your peers who shall prove it upon you, and slay you or thrust you out of the lists, or make you confess it in your throats.
And Diego Gonzalez his brother arose and said, You know, Sir, what perfect men we are in our lineage, and it did not befit us to be married with the daughters of such a one as Ruydiez; and when he had said this he held his peace and sate down.
Then Martin Antolinez of Burgos rose and besought the Cid that he might be another, and the Cid granted his desire, and said that he should do battle with Diego Gonzalez the younger brother.
Martin Antolinez and Diego Gonzalez brake their lances on each other, and laid hand upon their swords.
And Diego Gonzalez was sorely dismayed therewith, and though he had his own sword in his hand he could not for very fear make use of it, but he turned his horse and fled: and Martin Antolinez went after him, and dealt him another with the flat part of the sword, for he mist him with the edge, and the Infante began to cry out aloud, Great God, help me and save me from that sword! And he rode away as fast as he could, and Martin Antolinez called out after him, Get out, Don Traitor! and drove him out of the lists, and remained conqueror.