Alonzo is a black and white tom, and is often considered the 'second-hand-man' to Munkustrap. He saves Demeter from Macavity, and is the first to attack him after he defeats Munkustrap.
In the US and the first German Productions, he is depicted as being black and gold.
Alonzo is the most flirtatious of the cats; seen flirting with many of the kittens and queen cats. He acts cocky and arrogant around the male cats, and mischievously calls to the females. (Rum Tum Tugger seems to get more female cats attracted to him, but he typically blows them off instead of flirting like Alonzo.)
In the video, Alonzo can be seen dancing with quite a number of the queens. His duties always come first, though, as can be seen when he frightens away Grizabella in "The Jellicle Ball", when he rescues Demeter, and when he takes over fighting Macavity after Munkustrap falls. In the end he also tried to touch and accept Grizabella back to the tribe.