Martinet stated that the cornerstone of Waluigi's personality is one of self-pity, a character who feels that everything goes right for everyone but himself. Waluigi was created to be the tennis partner of Wario in ''Mario Tennis'' and early material from [[Nintendo of Europe]] portrayed them as brothers,<ref name=TheGamer/> but their relationship has since been ambiguous.<ref name=Waluigi2022/><ref name=":7" /> When asked whether Waluigi was a brother to Wario in 2008, Martinet stated that while he did not know, he felt that they were just "two nice, evil guys who found each other".<ref>{{Cite web |date=September 15, 2008 |author=David Oxford|title=Charles Martinet Celebrates 15 Years of Wario with Kombo |url=http://wii.kombo.com/article.php?artid=12729 |url-status=dead |archive-url=https://web.archive.org/web/20100509085022/http://wii.kombo.com/article.php?artid=12729 |archive-date=May 9, 2010 |access-date=October 1, 2009 |publisher=Kombo.com}}</ref>
Despite having appeared in more than 50 video games, Waluigi has been provided with little backstory and has few defining traits other than the need to be liked, an appreciation of [[Princess Daisy]], and his habit of screaming out his signature catchphrase, "Waaah!".<ref name=":2">{{Cite web |date=2018-06-25 |author=Clayton Purdom| title=Get to know Waluigi, the Nintendo character everyone loves to shit on |url=https://www.avclub.com/get-to-know-waluigi-the-nintendo-character-everyone-lo-1827112973 |access-date=2024-01-19 |website=The A.V. Club |language=en |archive-date=January 19, 2024 |archive-url=https://web.archive.org/web/20240119180121/https://www.avclub.com/get-to-know-waluigi-the-nintendo-character-everyone-lo-1827112973 |url-status=live }}</ref> In various ''Mario'' sports games Waluigi can perform exaggerated athletic moves. In ''[[Mario Power Tennis]]'' when making an offensive power shot, he demonstrates his spinning ability and poses in the shape of his "Γ" symbol. In ''[[Mario Party 8]]'', his preferred victory stance involves producing a rose as a recurring accessory.<ref>{{Cite web |author=Chris Compendio| title=Waluigi's Finest Moments |url=https://www.pastemagazine.com/games/waluigi/waluigis-finest-moments |access-date=2024-01-22 |website=Paste Magazine |language=en-US |archive-date=January 22, 2024 |archive-url=https://web.archive.org/web/20240122233957/https://www.pastemagazine.com/games/waluigi/waluigis-finest-moments |url-status=live }}</ref> As displayed in ''[[Mario Power Tennis]]'' and ''[[Mario Hoops 3-on-3]]'', Waluigi has the ability to summon a body of water and swim towards the ball, which ''[[IGN]]'' editor Rob Burman described as "baffling".<ref name=":6">{{Cite web |last=Burman |first=Rob |date=February 9, 2007 |title=Mario Slam Basketball UK Review – Nintendo DS Review at IGN |url=http://ds.ign.com/articles/763/763087p1.html |url-status=live |archive-url=https://web.archive.org/web/20101212015651/http://ds.ign.com/articles/763/763087p1.html |archive-date=December 12, 2010 |access-date=June 12, 2010 |website=[[IGN]]}}</ref>