Anguirus

Physical
Anguirus is a large, armadillo-looking creature. He has a crown of horns on the back of his skull, and the shell on his back is covered in spikes. The end of his tail has four spikes jutting out of it, and he is quadrupedal in nature.

Roar
Since Anguirus has yet to have a movie appearance in the Monsterverse, we don't know what he sounds like. In the comics, his roar is spelled "Mraaawr" for his normal roar and "Reeeawr" when he charges.

Personality
Anguirus is very close to the ground in his personality, and he shows a lot of care and concern for his best friend, Godzilla. Before Anguirus even became friends with Godzilla, he jumped in to defend him from a larger, unidentified monster in the GKoTM comic. Godzilla often uses Anguirus as a weapon, grabbing his tail and swinging him around like a flail, or kicking him while he is rolled into a ball. While this must hurt Anguirus, he doesn't seem to mind, as he shows no expression of pain.

Godzilla Permian period (Comic)
Anguirus appears alongside Godzilla as younger versions of themselves as they explore the Precambrian period and fight off monsters, including Megaguirus and an unidentified monster.

Ghidorah, the Three-Headed Monster (Comic)
Anguirus fights alongside Godzilla against Ghidorah during 1841, and helps his friend seal Ghidorah away in an iceberg.

Godzilla: Through the King's Eyes (Book)
Anguirus is mentioned to appear in some of Godzilla's PTSD-triggered nightmares.

Godzilla: King of the Monsters (Movie)
It was confirmed by Michael Dougherty that the monster bursting out of the ground is NOT Anguirus, thus ceasing the rumors of his appearance in the movie.

Godzilla VS Biollante (Book)
Anguirus has a small appearance in the first chapter, where Godzilla consults his friend about a nightmare he had involving the MUTOs. The conversation is short, and it is Anguirus' only appearance in the book.