The central register is the largest pictorial area on the Temple Side of a Yaxchilan stela, and displays a profile view of a historical ruler performing a blood sacrifice. A robed figure with a snaggle-toothed or bird headdress kneels at the feet of the ruler.
Blood sacrifices by royalty were done on Period Endings and accession anniversaries. The illustrated event on Stela I is the Period Ending 220.127.116.11.0. The ruler always wears what Carolyn Tate has identified as a "Period Ending" costume.