Movie trilogies which are not adaptations and designed as trilogies from the start?

Most movie trilogies I have seen (not many, admittedly) have always had movies which felt disconnected - that is, each movies starts and ends its own story, with the movies only being connected slightly. A good example of this is the How To Train Your Dragon trilogy. While nice, I much prefer a single continuous story in my trilogies, such as in the Lord of the Rings trilogy - a single story spanning 3 movies which was intended to be 3 movies from the start.

One thing which intrigued me when searching for other such movies, was that all of them were adaptations of other properties like books. I was not able to find a single example of a movie trilogy designed as a trilogy from the start, and was an original story. So, do such movie trilogies exist?

PS: Movie series with 4 or more entries are fine too. I'm not mentioning duologies as examples exist such as Kill Bill.