Katsuhiro Harada was recently compelled on X to clarify his troubled history with Tomonobu Itagaki, the creator of Dead or Alive and the 3D Ninja Gaiden games.
For the average person, the familiarity starts and ends with Itagaki's rather inflammatory comments about Tekken that he made well over a decade ago. He famously loved to talk smack about the series, and went as far as to say that his top 5 hated games are Tekken, Tekken 2, Tekken 3, Tekken 4, and Tekken 5.
Worth noting that this was a rather one-sided trash talk, and neither Harada nor Tekken ever truly retaliated against any of Itagaki's remarks. These days, most people understand that it wasn't all that serious, and even Harada himself mentioned that he misses some of the old-fashioned ribbing.
However, it goes so much deeper than that, as Harada explains in the post. Despite opening it with an extensive warning about the length of the post, it's a fairly breezy yet informative read about their history and the relationship between Tekken and Dead or Alive.