Final answer:
Mr. Rochester married Bertha Mason for her wealth and social position, deceived about her mental health by his own family who wanted the Mason fortune.
Step-by-step explanation:
Mr. Rochester married Bertha Mason primarily because he was tricked into the union for her wealth and social standing. The marriage was orchestrated without Rochester being fully aware of Bertha's hereditary mental illness, and he was persuaded by his father and brother who were interested in the Mason family's fortune. Over time, the marriage became a source of regret and shame for Rochester as Bertha's condition worsened, ultimately confining her to the attic of Thornfield Hall, which becomes a pivotal part of the plot in Charlotte Brontë's novel Jane Eyre.