Having met several times through the years, first as time-lost mentor Superboy to a Clark Kent of the 1930s, to the time when both battled each other before teaming up versus Aquarius, to the countless team-ups alongside their Justice League and Society compatriots, to their literally combining in body and mind to vanquish the evil Krogg. How would they handle their greatest threat, the malignant malice that is the Luthors, Lex and Alexei?
This happened when Lex traded places with his counterpart, dueling with Earth-Two's Superman while Alexei handled his own foe on Earth-One. Still, despite the element of surprise, the geniuses were unable to topple their mighty opponents. In each case, it was a courageous Lois Lane who faced the Luthors when the prospect of their great loves' lives were at stake. With this fresh in their mind, it was time for a heart-to-heart between the Men of Steel.
However, the deep dialogue of dedicated do-gooders was detracted by a determined Alex Luthor of Earth-Three, for it seems his own two counterparts were now operating on his world with the goal of merging Earths One and Two in one physical space...destroying them both! After an encounter with a mentally deficient Ultraman, who couldn't measure up to his two heroic cosmic twins, it was up to pair of planetary protectors to prevent the mad schemes of their arch-foes.
While the now weaker Kal-L faced off against Lex and Alexei, showing his dogged determination in the face of superior numbers and technological force, Kal-El prevented catastrophe by preventing an ionic energy beam from causing untold destruction to two sets of humanity.
In the end, Kal-L returned to his loving bride and the comfortable confides of his own Metropolis, Kal-El returned to a life where he was separated from those he loved by the weight of his monumental duties. Would time cause him to allow for the "man" to supercede the "super" as it had his counterpart, or would he continue to persist in his lonely life since his days as a young Boy of Steel? Alas the Crisis on Infinite Earths prevented a definitive answer.
And yet, we're not done as there were even further meetings between these paragons of power...