My ISTJ father has the following traits...
-Very dependable. If he says he's going to do something, he will do it. If he makes plans, he will honor them/
-Dark sense of humor... which makes him hilarious at times.
-Extremely intelligent. I cannot and now outright refuse to debate with him because I can never keep up with the factual information he throws at me. He's also really good with remembering details that nobody else pays attention to & tends to use them in debates. He is highly interested in a few subjects - mainly history, politics, and religion. I'd consider him an unofficial expert in these subjects as he knows them better than anyone else I know.
-Family oriented. We've had a few bumps along the way, but any distance I took from him has been MY decision. He has never shut me out & always been there when I came around after shutting him out. He values me as his daughter, despite not understanding me at all. I remember the last time I contacted him after a long time of not communicating. Sure he said his peace about the situation, but that was after he immediately welcomed me back into his life.
-He's a quiet guy, but can hold his own in conversation with close friends. He values his solitude, however, and takes daily hikes near his home to clear his head. He values "inner peace" highly and works to maintain it.