Valve Corporation is a software developer company known for several video games franchises including Portal, Half-Life, Team Fortress, Left 4 Dead, Counter-Strike, Defense of the Ancients/DOTA, and Day of Defeat. They are also known for their Steam program, which is a online network for PC gaming that is used for digital game downloads and interacting with other users. They also created the Source Filmaker software, which is a popular tool used by YouTubers for making short videos, and they have used it themselves to make promotional videos for Team Fortress 2.
Valve was founded in 1996 by former Microsoft employees Gabe "Gaben" Newell and Mike Harrington, and became a well-known developer with their first game, Half-Life, before focusing primarily on PC gaming. Portal happens to be a spin-off of the Half-Life series, which is made clear through the mentioning of Black Mesa in Portal, the fictional company that Half-Life protagonist Gordon Freeman works for.
They licensed the use of the Portal franchise to Warner Bros. for LEGO Dimensions, marking their first time they have worked with LEGO and Warner Bros.
Ironically, even though Valve is known for working primarily on games that are exclusive to PC platforms, LEGO Dimensions is not available for PCs.
Since LEGO Dimensions was released for the Wii U, it marks the first game with Valve-owned content to appear on a Nintendo platform.