Morpho helenor, sometimes also called the Common Blue Morpho, is a neotropical butterfly found throughout Central America and south to Bolivia.
There are around 30 subspecies.
Morpho helenor (and its close relative Morpho achilles) are recognised by the broad vertical bands of brilliant blue on their uppersides, and by the distinctive white, black, yellow and red concentric rings which form the ocelli on their olive-brown underside hindwings.
The size of these ocelli, and the width of the blue bands on the upperside, varies considerably.
In flight, this species shows its very large shiny blue wings which follow a slow bouncy flight pattern.
In rest, however, it is so much less visible because of the dark brown underside of the wings.
This is the subspecies Morpho helenor octavia which occurs in south-west Mexico (Chiapas) to El Salvador.

Andrew Neild, author of The Butterflies of Venezuela and a recognized authority on Neotropical butterflies, helped me identifying this butterfly.

1st & 2nd photo: El Triunfo Biosphere Reserve, Chiapas, Mexico, 21 April 2011
3rd photo: El Triunfo Biosphere Reserve, Chiapas, Mexico, 25 April 2011