The Hulk is regarded as one of the strongest characters in the Marvel Universe with the power to quite literally smash dimensions. That said he wasn’t always this strong and there have been times when he was thoroughly trounced by other characters.
Asgard’s god of thunder possesses enough physical strength to destroy planets if he wants so it’s no surprise that he can stand up to the hulk. In a close fight in the 2001 issue thor hit the green beast with a lightning bolt to the back of the head that knocked him unconscious for a few moments.
Juggernaut is a mutant with power similar to the Hulk, the two fight time and time again but juggernaut has been able to score a victory on several different occasions, the most known being in the incredible hulk vol.2 when hulk is in the Amazon rainforest investigating strange happenings.
Juggernaut attacks him during this time because he knew that hulk was in his professor form (drawing power from his intellect rather than anger). Juggernaut took advantage of this flaw to defeat the hulk beating him mercilessly into the ground.
Namor is the king of everything under water and also the first mutant Marvel created but not the first chronologically.
When underwater, Namor is practically invincible, his strength is unmatched as Hulk learns in Avengers no.3. Namor takes hulk out with practically a single punch before tossing him into the water and submitting him into a whirlpool. Hulk never landed a punch.
As his name might suggest, apocalypse is the strongest of the mutants and also one of the most ornery. Between his power to manipulate his own molecules and his power to throw his opponent’s powers back at them, hulk would be fighting a losing battle.
Not to mention that apocalypse already beat Hulk once and recruited him as one of the four horsemen.