There is nothing known about Lopez's appearance.
Lopez seemed to value the legendary gun and didn't want anyone else to have it in their possession.
One Piece: World Seeker
After Luffy, Nami and Jeanne find the treasure chest that contains the gun, it is revealed to be empty, but a letter is left inside. In the letter, Lopez says that whomever had wanted the gun cannot have it as it is precious to Lopez and they should reflect upon their adventures, as the experiences they have gained either equals or surpasses any benefits the gun could offer.
- One Piece World Seeker Chapter 8: The Old Island - Lopez is mentioned.