Fenrir

Loki's first son assumes the shape of a small black dog. His true identity is that of the Fenrisulfr, a giant wolf bound by the gods. Fenrir enjoys food and taunting Yamino. A running gag in both the anime and manga is how Fenrir can be very bossy and intentionally crude around Yamino, then instantly become the most affectionate and harmless puppy-son possible the moment "Daddy" walks in (during the series, he has an almost scary Father Complex. He's very outwardly protective of Loki, spouting threats when Loki may be in danger). While the gods can understand his words, it would appear that when a human hears him talk all they hear is a regular dog (though his barking sounds like he's singing).