At launch, Terraria was a much simpler game compared to the content-heavy "Journey's End" updates players are familiar with today. It focused on a "small, dense, and fun sandbox experience" where the ultimate goal was relatively straightforward.
There was no Hardmode in version 1.0.0. The game featured only a handful of bosses: Eye of Cthulhu Eater of Worlds Skeletron (widely considered the "final boss" at the time) King Slime terraria 1.0.0