Itzamná (God D)

In the Postclassic Period codices, this god used to be called (and in some books still is) god D. Worshiped at least as far back as the Preclassic Period, Itzamná -- a name spelled various ways -- was a god whose name translates as "one who does itz." ("Itz" seems to be a word that means any sacred liquid -- such as water, sap, and blood.)

Itzamná was the first shaman and a creator god (though some books say that he was an aspect of a creator god or one-half of a god.) He had a lot of avatars, was connected with various things such as rulers, writing and possibly god N.  He also seems to have connections to the gods of rain, corn, and the sun as well as the world tree.

History of Importance
As history passed, Itzamná became a very important god to the ancient Maya. Then the Classic Period collapse happened, and he became less important. His importance went down because the Maya had begun to stop believing in rulers that were connected to the gods -- they were switching to councils. Later on, in the Yucatan Peninsula, Itzamná's importance increased again.

Appearance
Itzamná appears to be elderly and male. His nose is big, and a description you may see of it is "Roman." The shape of his eyes was drawn either square or round, depending on the artifact.There are also certain things the ancient Maya tended to draw as part of their depictions of Itzamná. One is his headdress, which has a flower with an ak'bal symbol (ak'bal means dark/night) in it. Another thing they tended to show him wearing was a necklace made of shell.

Art with Itzamná in it shows him doing things like creating the sky or being a ruler that's managing a ritual. Also, it was common for the ancient Maya to draw him sitting on a throne.

Function
Among other gods, rulers may have looked to Itzamná's supernatural court as something to imitate as a form of 'correct' behavior. If true, this included how they set up their cities as well as how they acted themselves. (It seems that other gods' lives were possibly imitated as well.)

Quirigua's Stela C appears to be an example of the belief that Itzamná helped make the current world. It seems like the stela says that Itzamná -- which the stela calls Six Sky Lord -- and three other gods set three "throne stones" for a hearth in the sky. (Itzamná's throne stone was the water or waterlily throne stone.) Part of this stela also shows Quirigua's Ruler I in a ceremony, dressed up as Itzamná -- dressing up as gods as part of rituals was something the Maya did, and one of the gods they're known to have imitated in rituals was Itzamná. (There's a theory that rulers used quetzal feathers as part of their headdresses to copy the Principal Bird Deity, one of Itzamná's aspects.)

The ancient Maya in the Postclassic Period went to him (among certain other gods) when the coming year was predicted to be an unfortunate year, with disasters such as crop failure. They would ask him to keep the year from having disasters.

Itzamná was a god of scribes -- and he was a scribe himself. He was also a god of knowledge.

This god was also connected to some more pointedly mystical things. One of these was foretelling the future. The other was the ability to look at things that you couldn't normally see as a person.

Curiously, it seems Itzamná had a bad side too. This negative part of him would destroy crops.

Aspects
Four aspects of Itzamná are a peccary, a turtle with a k'an sign on its shell, a possum, rattlesnake and the crocodile-like creature that makes up the earth -- that is, the part that people live on, in between the upperworld and underworld. (There is a theory though that Maya art that shows animals as being the land on which people walk should not be taken literally.) Itzamná also has a group of four aspects, each connected to one of the four cardinal directions and a color. And another aspect of his was the Milky Way.

The goddess Chak Chel (you might come across books that refer to her as Ix Chel) may be an aspect of Itzamná, or perhaps they were two parts of one deity. The ancient Maya may have given Itzamná and Chak Chel credit for being the creators of people as well as time. The two may have been seen as the gods of healing as well.

In the Classic and Postclassic Period at least, another aspect  -- or perhaps spirit animal companion -- of Itzamná was a supernatural bird that has the same headdress as him. Images of the bird also tend to have it holding a snake in its beak. Archaeologists sometimes call this bird the Principal Bird Deity (PBD for short) or the Itzamná bird. Because of how it looks, there's a theory that this bird's appearance may have been based off of a real species of bird called the laughing falcon or guaco (Herpetotheres cachinnans) -- but not everyone agrees on what bird the Principal Bird Deity is supposed to be like though. 

(There's a also theory that  Itzamná (god D) is actually a a mix of of Pauahtun (god N) and the Principal Bird Deity.)

Consideration
Itzamná tends to be drawn with a hummingbird. In these images, the hummingbird is giving him things. This may mean that the hummingbird was Itzamná's messenger. It's not the only possible messenger of this god's though. Archaeologists have found evidence that there were times where the Principal Bird Deity delivered messages for Itzamná. The name for the Principal Bird Deity as a messenger could be Muut Itzamnaaj.

References:

Google Books: "Philosophy of the Ancient Maya: Lords of Time"; Alexus McLeod; 2018

Google Books: "Art and Myth of the Ancient Maya"; Oswaldo Chinchilla Mazariegos"; 2017

The SAO/NASA Astrophysics Data System: "High-resolution speleothem record of precipitation from the Yucatan Peninsula spanning the Maya Preclassic Period"; Medina-Elizalde, Martín; Burns, Stephen J.; Polanco-Martínez, Josué M.; Beach, Timothy; Lases-Hernández, Fernanda; Shen, Chuan-Chou; Wang, Hao-Cheng; March 2016

Google Books: "The Origins of Maya States"; Loa P. Traxler, Robert J. Sharer (editors); 2016

"Dreams in Mayan Spirituality:Concepts of DreamingFrom the Ancient Mayans to the Contemporary Mayans around Lake Atitlán"; Elena Levi; March 2010

"Re-Creating Primordial Time: Foundation Rituals and Mythology in the Postclassic Maya Codices"; Gabrielle Vail, Christine Hernández; 2013

"Maya Sacred Geography and the Creator Deities"; Karen Bassie-Sweet; 2008

"Mortuary Landscapes of the Classic Maya: Rituals of Body and Soul"; Andrew K. Scherer; 2015

Five College Compass Digital Collections: "Birds and Environmental Change in the Maya Area"; Peter Stuart (with contrib. by David Stuart; 2015

The University of Texas at Austin: Texas Scholar Works: University of Texas Libraries: "Framing the portrait : towards an understanding of elite late classic Maya representation at Palenque, Mexico"; Kaylee Rae; 2007

Journal of Ethnobiology 32(1): 74-107: "Water Lily and Cosmic Serpent: Equivalent Conduits of the Maya Spirit Realm"; J. Andrew McDonald, Brian Stross; 2012

eScholarship: "A Study of Classic Maya Rulership"; Mark Alan Wright; 2011

Digital Collections at Texas State University: "Maya Scribes who would be Kings: Shamanism, the Underworld, and Artistic Production in the Late Classic Period "; Barry B. Kidder; 2009

FAMSI: "Maya Hieroglyphic Writing: Workbook for a Short Course on Maya Hieroglyphic Writing", Second Edition; 2011

"Maya Calendar Origins: Monuments, Mythistory, and the Materialization of Time"; Prudence M. Rice; 2007

"Water and Ritual: The Rise and Fall of Classic Maya Rulers"; Lisa J. Lucero; 2006

"Reconstructing Classic Maya Economic Systems: Production and Exchange at Cancuen, Guatemala"; Brigitte Kovacevich; 2006

"Landscape And Power In Ancient Mesoamerica"; Rex Koontz, Kathryn Reese-Taylor, Annabeth Headrick; 2001