The original Apple TV (A1218) was first show off in September 2006 and referred to as the iTV. It made its official debut at Macworld Expo in January 2007 alongside the original iPhone.
Based on a stripped down version of OS X Tiger originally called "lobot" (short for "lobotomized, it had a 40GB hard disk inside — eventually a 160GB hard disk — and served primarily as a way to sync content from iTunes on the desktop and play it on the TV. It was limited, but it was... something. It had both HDMI and component video in, and supported up to 720p, as well as optical and RCA audio. 10/100 BASE-T ethernet and up to 802.11n Wi-Fi allowed it to connect to the network. It also had a USB 2.0 port, though never for anything more fun than servicing.
Apple kept it around as a hobby until they replaced it with the second generation, completely redesigned and re-architected, Apple TV 2 in September of 2010.