Final answer:
Stan Lee is the actor who appeared in nearly every Marvel movie. He often made cameo appearances but did not play a continuous character.
Step-by-step explanation:
The actor who played a role in nearly every Marvel movie up to Endgame is Stan Lee. Stan Lee, the co-creator of much of Marvel's universe, frequently appeared in a brief cameo role in Marvel's movies. It's worth noting however, that he did not play a continuous character but rather different bit parts in each film.
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