Memento Mori. Most people in history community will know, but it means "remember your death", and it was allegedly something Roman emperors or generals made sure to have someone whisper into his ear during the celebrations of him.

A lot of things that look absurd in history are just a mortal man who had done great things being mortal. In the end we're all going to die, it's the great equalizer.

In the end, then, the question stops being about trying to achieve literally mortality by being great, and instead making sure that the life that you lead is great and that the thing that you leave behind is great. Because as we've seen, great kings can die from a bad swim, mighty emperors can fall to a single bullet, men who conquered the known world died to some bad booze, and feats alone don't stop those things.