Image Credit: Lucasfilm
Pao is a Drabata, an amphibious species that is new to the Star Wars Cinematic Universe. He is a fierce commando and will charge into battle against the Empire, all the while, shouting his native and customary battle cry of:
“Sa´kalla!”
Rogue One director Gareth Edwards had this to say about Pao’s creation and design:
"“There was this great design of this creature that’s mouth would open really wide, and he looked like he was really good at giving orders and shouting at people during a battle. I was like, ‘We’ve got to give him that moment in the film,’ and so [Pao] was born out of that."
Looks like he nailed that design, perfectly.