While fans of in the same body before Marc Spector - and he gets stronger with every one. Bruce Banner's psyche is just as fractured as Spector's - in some interpretations even before his origin story - and has spent significant time in comics attempting to control his identities. The journey of the Hulk's identities is as memorable as Moon Knight's, and is always tinged with darkness.
Moon Knight's alternate identities didn't originate as separate personalities. Adventurer and mercenary Marc Spector simply created them to better serve his crimefighting endeavors. He made Steven Grant to make connections with the wealthy elite while also allowing himself a method of funding his Moon Knight activities, and he created Jake Lockley to connect with informants in the underworld. These were eventually retconned into entirely separate alternate personalities - and while Hulk initially started out the same way, the paths of the two heroes divulged dramatically.
The Savage Hulk is the most well-known incarnation of Bruce's alter ego; he's impossibly strong, incredibly quick to anger, speaks in simple, declarative statements and only wants to be left alone. But he wasn't technically the first Hulk - that honor goes to Joe Fixit, the grey Hulk and the version of the character first seen in The Incredible Hulk #1 in 1962 (and Hulk #347 for the modern-day incarnation). Fixit is a hybrid of Steven Grant and Jake Lockley: a violent, streetwise mob enforcer who prefers fancy suits, well-made drinks and other expensive tastes.
Other personalties of the Hulk soon followed: the Professor, otherwise known as the Merged Hulk, has Bruce Banner's genius-level intellect and the Savage Hulk's strength, and the Green Scar is the super-strong variant seen in the Planet Hulk and World War Hulk series (hell-bent on revenge after his family is killed by the Illuminati, or so he believes). The most dangerous personality of Bruce's by far is the recently-appearing Immortal Hulk: an immensely powerful, vengeful giant who simply cannot be killed in any way.
Bruce's split personalities often change regarding their functionality. Usually, the entities have separate memories, although Bruce can occasionally sense what his other personalities are doing. Oddly enough, this is another Moon Knight parallel, in which the four major alters aren't always aware of each other's actions. Regardless, the Incredible Hulk was split long before Moon Knight, and the former might have even influenced the latter in of stories and characters involving multiple personalities in one body.
