Romanticism was a reaction against an emotionless rationality and structured literature that defined the Age of Enlightenment and Reason. Faust personifies this dichotomy on his way to becoming the Romantic hero. Faust starts out as a respected and admired representative of rationality and structure as a quiet-living academic who is an expert in every field of study from Mathematics to Divinity. Faust has spent his life in the pursuit of knowledge, which precluded (i.e., made impossible) involvement in life's pursuits of happineess, pleasure, and feelings.
Now, having found that the knowledge available to him is in the end analysis meaningless ("And see, that nothing can be known! / That knowledge cuts me to the bone."), he is searching for the knowledge of the cosmos "That [he] may detect the inmost force / Which binds the world, and guides its course." He wants to transcend the limits of earth's hold on mortal flesh and with the Moon
on mountains grand,
Amid thy blessed light ... stand, ... [and]
Float [as molecules] in thy twilight the meadows over,
After his encounter with Mephistopheles (Mephisto), Faust is persuaded to wager that Mephisto cannot lure him from his quest by vain pleasure and passion. His wager with Mephisto, which grows bit by bit from the initial,
Canst thou with lying flattery rule me,
Until, self-pleased, myself I see,—
Canst thou with rich enjoyment fool me,
Let that day be the last for me!
ends with a complicated challenge to Mephisto to tempt Faust and distract him through life's feelings:
Let us the sensual deeps explore,
To quench the fervors of glowing passion! ....
Then may delight and distress,
And worry and success,
Alternately follow, as best they can: ....
This is where Faust symbolically leaves behind the rational approach of the Age of Enlightenment and Reason and becomes the Romantic hero. In his new persona--as the Romantic, feeling, passionate hero--Faust engages in lust and murder and horror and despair when he seduces Gretchen (thanks to the motivation given by Mephisto's magical potion), then murders Gretchen's brother Valentine (while under Mephisto's control), then suddenly learns with rage about Gretchen's murders and imprisonment, then fails in earnest and heart-wrenching attempts to rescue her from execution. In Faust Part II, Faust becomes a Classical hero and is no longer a Romantic hero because Goethe renounced Romanticism in 1777 and pursued Classicalism thereafter.