Pixel was the name of Google’s first smartphone designed and sold under its own Pixel brand.
Google announced the first-generation Pixel and Pixel XL in October 2016. The smaller model was simply called Pixel, while the larger version was called Pixel XL. Both phones were positioned as Google-designed hardware with close integration between Android software and Google services.
Before Pixel, Google had sold Nexus-branded phones made in partnership with manufacturers such as HTC, Samsung, LG, and Huawei. The Pixel launch marked a shift toward Google controlling more of the hardware and software experience, although manufacturing was handled by HTC for the first generation.
The answer is specifically Pixel, not Pixel XL, because the question asks for the first smartphone in the brand rather than the larger companion model. Later generations added numbers, beginning with Pixel 2.