Jack (ジャック, Jakku?) is a main character in Beastars. He is Legoshi's close childhood friend. 

Jack is a Labrador with a slender build, light yellow fur, and large brown eyes. He is typically seen wearing his school uniform, which consists of a white dress shirt with rolled-up sleeves, an indigo vest, a dark gray tie, black suspenders, gray pants with dark gray vertical stripes, and brown loafers. During the warmer seasons, the top-wear is replaced by a blue polo shirt. Jack also started wearing Legoshi's old clothes when Legoshi dropped out of school, even though they were too big for him.