As the story goes, Jor-El is Superman’s biological father, and a leading scientist on the planet Krypton before it's destruction. He foresaw the planet's fate but was unable to convince his colleagues in time to save the inhabitants.
Jor-El was able to save his infant son Kal-El (Superman) by sending him in a homemade spaceship towards Earth just moments before Krypton exploded.
In Superman/Batman #50, it is revealed that, years ago, Jor-El sent a probe to Earth that made contact with Thomas Wayne (Batman’s father) while he was on a drive with his pregnant wife.
The probe holographically transmitting Thomas' consciousness to Krypton so that Jor-El could better learn what kind of world Earth was to help him decide which of many possible candidates he should send his son to.
Thomas tells Jor-El that the people of Earth aren't perfect, but are essentially a good and kind race that would raise the child right, convincing Jor-El to send Kal-El there.
Thomas recorded his encounter in a diary, which was discovered by his son Bruce Wayne in the present day.