It is no secret that the Joker is absolutely obsessed with Batman as he views himself as Batman’s perfect opposite who completes the Dark Knight just as much as Batman completes him. While that may be the case in later DC continuity, it wasn’t always–as the Joker’s earliest days as the Caped Crusader’s arch enemy proved that he was obsessed with one thing way more than Batman.
The Joker is something of an enigma in DC Comics as he has never had a solid origin story and doesn’t use a secret identity like most other DC villains. Instead, the Joker is seemingly a cosmic force of anarchy that has been set loose upon the Earth as he cares about nothing more than spreading chaos wherever he goes and can seemingly never be defeated despite being a mere mortal. The Joker is irredeemable, untrustworthy, and utterly toxic to anyone that comes near him–with Joker's treatment of Harley Quinn as the perfect example of his repugnance. As his character became more developed in DC Comics, his apathetic nihilism continued to shine brightly and his desire for money and power lessened greatly as he proved that he only ever wanted to corrupt the world around him with Batman acting as his ‘white whale,’ so to speak. However, upon his debut, the Joker was nothing more than a brilliant thief who wasn’t afraid to commit murder to get what he was truly obsessed with.
In Batman #1 by Bill Finger and Bob Kane, the Joker makes his villainous debut by announcing over the radio that he intends to kill a number of people at specific times and steal their valuable jewels and diamonds. While Batman eventually stops Joker, the Clown Prince of Crime is successful in robbing most of his recently deceased targets. Later that issue when he breaks out of prison, the Joker picks up right where he left off and starts stealing rubies and gems from people he is also murdering. Then, in the next issue after the Joker is presumed dead, the villain returns to once again steal valuable jewels, and a few issues later in Batman #7, he creates a whole gang of brainwashed goons for the purpose of stealing even more valuable gems.
Based on his earliest crimes, as well as how he viewed Batman at the time, it seems as though the Joker was originally way more obsessed with stealing valuable jewels, diamonds, and gems than he was with the Dark Knight himself. While this all could be viewed as a game Joker plays with Batman, that doesn’t seem to be the case–at least in these earlier issues. The Joker wants nothing to do with Batman when the hero swoops in to stop him, and the Joker works to kill him upon meeting him so that he can go back to gathering the rubies and gems that are so precious to him.
The Joker stealing those valuables seemingly gave him a sense of pride and superiority over Gotham’s police force, so getting them at all costs was his one and only mission. When Batman got involved, however, he threw a wrench in the Joker’s fun which made the Clown Prince of Crime genuinely hate the Caped Crusader as Batman kept the Joker from his prizes. While the Joker eventually grew to love Batman (in a sick and twisted sort of way) he originally wanted nothing more than to be rid of the Dark Knight so that he could focus on his true obsession: stealing valuable jewels right out from under everyone’s noses.