"Waluigi (ワルイージ Waruīji) is a fictional character in the Mario series of video games. He accompanies Wario in spin-offs from the main Mario series, oftentimes for the sake of causing mischief. He was created by Camelot employee Fumihide Aoki and is voiced by Charles Martinet, who describes Waluigi as being someone who has a lot of self-pity, feeling everything is going right for everyone but himself. Since he appeared in Mario Tennis, he has received mostly negative reception, described as one of the most unimportant video game characters ever made by GameDaily, as well as being called an abomination by Cracked."
Source: Wikipedia, "Waluigi", available under the CC-BY-SA License.