The House of El was a significant house (or family) on the planet Krypton before its destruction. Known members of the House of El were Jor-El, Lara-El, Kal-El, Zor-El, and Kara. Though some Kryptonians survived the destruction of Krypton by various means, Kal-El and Kara were the only survivors of the House of El, sent to the planet Earth in different spaceships before Krypton's destruction and Kal-El was raised there by Jonathan and Martha Kent as Clark Kent. However, Jor-El's consciousness did exist for a time as an artificial entity, first communicating with the young Kal-El through his spaceship, then through the Kawatche Caves and finally the Fortress of Solitude.
The House of El originally took as its symbol the Kryptonian symbol for "hope" (an infinity symbol rotated 90 degrees, resembling a figure 8, inside a Kryptonian pentagon) which also represents the letter "S" in the English alphabet. This symbol was burned into Clark's chest as part of a test by Jor-El. The House of El's symbol eventually evolved, with the insignia inside the Kryptonian pentagon resembling the Earth-English alphabet's "S."
It is known that at least one member of the House of El visited Earth before the destruction of Krypton. In 1961, Jor-El was sent by his father as a rite of passage. During his visit, he recorded his memories on a pendant belonging to the House of El. The pendant's design was based on the original symbol of the House of El, suggesting that it may have been passed down through many generations of the family.
Later, Jor-El created the Phantom Zone, a place to imprison Kryptonian criminals and other extraterrestrial creatures either in their physical form or in a phantom-like form (in which their physical body was destroyed). Before Krypton's end, Jor-El urged his assistant Raya to enter the Phantom Zone since she would have more chance of survival there. He gave her a crystal, bearing the symbol of the House of El, as protection against the prisoners there. Knowing that he had enemies, Jor-El ensured that should a member of the House of El ever become trapped in the Phantom Zone, their blood would open the gateway out. Clark Kent was forced to use this gateway when he became trapped there and the opening of this gate brought him and several prisoners of the Phantom Zone to Earth.
In the Comics
The House of El was greatly explored in the comics, especially a four-part comic arc including Superman researching his family history with Kara and Zor-El. The search went from Kandor to outer space, having Kal-El pick up space signals from the past, allowing Kara and Kal-El to view their ancestors. The earliest know ancestor of Kal-El II (Clark) is Feln, and the first El was Erok-El, Great-Grandson of Feln.