Luca is a territorial and aggressive watchdog with a strong dislike towards Garfield. Garfield's insults and tauntings often causes him to snap, but he is always tricked and humiliated by the obese feline. Needless to say, his greatest handicap is his lack of intelligence, as he even mentions at one point that he thinks math means spelling.
He does show a kinder and more playful side to him upon encountering Odie, as Odie's innocent nature appears to soothe him.
He doesn't seem to hold any grudge against Arlene and Nermal despite them being cats, as he was seen accompanying them later in the movie. Thus, proving that his hatred for Garfield was solely caused by the orange cat's insults.
- A recurring plot in Garfield comic strips involves Garfield picking fights with various watch-dogs. Luca is most likely an allusion to this.