Sumo is a Japanese sport where a wrestler (rikishi) attempts to force another wrestler out of a circular ring (dohyō) or to touch the ground with anything other than the soles of the feet. Sumo wrestlers are always incredibly large, just like this Monster is very large.
In the anime, when this card detaches an Xyz Material, it absorbs it through its nose.
"Sumo King" sounds the same as "Smoking" in japanese. This might be related to how, in the anime, the card inhales the detached Xyz Material and then blows out a beam that causes smoke to rise when it hits.