Whoops.. i wanted to like but j unliked it by mistake.. anyways.. I wanted to say that the Cesares are from different timelines. First js the contractor Cesare who Mc meets first and then later meets his younger version when she goes back in time. But between the present and the past she visited... this cesare is somewhere in between.
The demons have to change their name often so that others won't recognize them. They create new identities for themselves every couple centuries so that angels and humans kind of leave them alone.
Leviathan is his original name. Great Demons use those OG names more so as titles since they all go by so many different names.
Mars is the name he had 600 years ago.
And Cesar is the name he had for the last century.
Lillith is the title that was passed down to Catherine by her mother since she is the keeper of the void now.
Mars never met Catherine as Lillith, but I suspect he knows that "Audrey" (Catherine's form and stolen identity) IS Lillith, if not Catherine. He probably senses she's another Great Demon by his glance back at her.
Leviathan once said that while they DO remember everything from the past, they don't keep everything in their head until they need that information since they live for so long. Catherine asked him why didn't he remember meeting her in the past as Mars, and that was his explanation. He didn't remember until after she became Lillith.
But he DID remember this meeting, and he apologized ahead of time for his behavior before she went to the past again. Which is kinda funny

what’s happening i know mars and cesare are the same but not really so someone please explain