Word to describe a person who is always very stable

What do you call someone who's very stable all the time? By that I mean someone who never lies, manipulates or cheats. Someone who doesn't understand jokes sometimes, and someone who never gets overly excited. But not someone who's boring. He just has a calm atmosphere. There may not be a word for it, but I want to know how I could describe someone like that.

Solution 1:

I've always used the term "straight arrow" to refer to such a person, especially if I wanted to emphasize the "never lies, manipulates or cheats" aspect. The "doesn't understand jokes sometimes, and never gets overly excited" part follows (to some degree) from always acting in a responsible and upright manner.

https://dictionary.cambridge.org/us/dictionary/english/straight-arrow

https://www.collinsdictionary.com/us/dictionary/english/straight-arrow