The character sculpts and ingame models shown below are fan art renditions of classic Street Fighter characters, sculpted digitally and modded into Street Fighter IV and Street Fighter V respectively.
 
All character designs are originally © Capcom.
 
Chay Johansson took care of the in-game cloth physics setup and beauty poses.
SFIV / SFV MODS
Alex mod

Replaces Abel in SFIV and later Alex in SFV with an Alex model created from scratch, in the likeness of the SFIII portrait illustration of the character.
Funnilly enough a composite screenshot of the sculpt placed in context was picked up by a gaming news outlet to illustrate the rumour around the official addition of the character in SFV.

Ken head mod

Replaces the default SFV Ken head and hair with a custom model inspired by the classic look of the character and the likeness of the Street Fighter Legacy actor Christian Howard, and also introduces a "Maximilian Dood" variant with glasses and beard. The in-game body is left untouched.
This head model was created with all respect for the original artist who had to work with the real constraints of production and art direction. Fan modding provides a freedom that real production doesn't allow.

Q mod

Replaces Dictator in SFV with a model of Q created from scratch. I believe the mod was later ported to G by the community.

Twelve mod

Replaces Ryu in SFIV with a model of Twelve created from scratch.