In response to a question from a fan regarding which Tekken characters would never return, Tekken producer Katsuhiro Harada revealed that he will never come back as an in-game character. While the statement was likely meant to be humorous, Harada has made appearances in Tekken, as well as some other titles he worked on, making him one of the few developers featured in their own games.

Harada used to voice multiple Tekken characters behind the scenes
Harada has served as the Japanese voice actor for Marshall Law in the original Tekken up until Tekken 7 and provides the battle grunts for all iterations of the character except his Street Fighter X Tekken appearance. He also provides the voice for Marshall’s son, Forrest Law, in his playable appearances in Tekken 3, Tekken Tag Tournament, and Tekken Advance.
Outside of the Law family, Harada was the original voice of Yoshimitsu up until Tekken Tag Tournament and the female ninja Kunimitsu in the original Tekken. While later Tekken titles reuse some of his previous Law grunt recordings, Harada says he cannot do voice-over work anymore on account of his age.

Harada has made cameos in Tekken promotional material and games
When it comes to physical appearances, Harada has made a cameo appearance in a Tekken Tag Tournament 2 loading screen as well as several Tekken 7 DLC trailers, including those featuring guest characters such as Fatal Fury’s Geese Howard and The Walking Dead’s Negan. His appearance in Tekken 7 can also be recreated using the “Bearded Man” cosmetic pack and character customization features.

Recently, Harada can be found in Tekken 8’s Arcade Quest single player mode. While his avatar does not talk, it bears his likeness and can be fought at the Final Round area. Defeating Harada’s Feng awards you with the “Godfather” achievement as well as in-game currency and customization items.

Harada is a guest fighter in Soulcalibur V
Outside of Tekken, Harada’s contributions as a member of Project Soul (the team responsible for Soulcalibur) earned him an appearance in Soulcalibur V as a fightable character. Donning an outfit similar to Heihachi Mishima’s and using Devil Jin’s Tekken combat style, Harada is a unique opponent who, once beaten, awards the “Pursuit of Obsession” achievement.
Some fans seem disappointed that Harada will probably never be featured as a playable character. Given the number of fan requests and previous cameos, some were hoping that an out-of-pocket decision such as including a playable developer would help mix things up. With legacy fighter Armor King and newcomer Miary Zo on the way, however, Tekken 8 players will have their hands full learning new movesets instead of thinking about Harada’s absence in the roster.