Michael LaFosse is known for his origami butterflies and I think this Alexander Swallowtail Butterfly is by far the most beautiful of his designs. His website features quite a few of his designs. In addition, the tutorial for this butterfly is also available there.

Though I am a beginner origamist, I found the tutorial to be very useful and in spite of the design being of the intermediate level of complexity, I was able to complete it quite easily, thanks to the detailed tutorial.

The butterfly can be done in a large number of sizes, from 2-3 inches square to 6 inches squares. Duo coloured paper works best, as it brings out the change in colour in the body of the butterfly.

If you are fascinated with origami butteflies, then the book, 'Michael LaFosse's Origami Butterflies is a great find. The book describes Michael LaFosse's system for folding an unlimited variety of origami butterflies. It is an absolutely fascinating book that starts by describing the variations for creating your own unique butterfly design and ends with the diagrams for some of LaFosse's beautiful butterflies including the Alexander Swallowtail and Alexander Aztec butterflies.

Model Details:

Model: Alexander Swallowtail Butterfly

Creator: Michael LaFosse

Book: Origami Butterflies
 
Authors: Michael G. LaFosse and Richard L. Alexander
 
Difficulty Level: Low Intermediate

Paper Ratio: Square

Paper Size: 5 inches

Model Size: ~5 inches in diameter

Tutorial: PEM Origami. To reach the tutorial, just go to the link -> Fold more models -> Origami Now! -> Butterflys.