In Dragon Age: Origins
"The mabari is clever enough to speak, and wise enough to know not to."If The Warden is a human noble: The Warden's warhound has a pedigree older than Highever, and a penchant for driving cooks to distraction.
If The Warden is not a human noble: The Warden found this mabari in the camp at Ostagar. His master was killed in the Wilds, and Dog fell ill from biting the darkspawn in battle. Dog seems to have chosen The Warden as his new master now, seeking The Warden out after the battle at Ostagar and warning of an impending darkspawn attack.
In The Darkspawn Chronicles
Barkspawn was a mabari hound who was found injured at Ostagar. Alistair saved the dog's life, and the two have been inseparable ever since. Why Alistair named the dog Barkspawn is anyone's guess.