ocw.mit.edu
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MIT OpenCourseWare (OCW) is a free, openly accessible repository of MIT course materials. It offers lecture notes, assignments, exams, and occasionally video lectures across a wide range of subjects, including mathematics and abstract algebra, for self-paced study of topics like group theory relevant to character theory.
More resources on Character Theory
Stony Brook Rep Theory Notes
Free notes on finite group representations and characters
nLab: Character
Comprehensive notes on character theory
mathworld.wolfram.com
MathWorld is a comprehensive online mathematics encyclopedia by Wolfram Research, featuring in-depth, well-structured articles on topics across math, including character theory within group theory. Each article includes definitions, theorems, formulas, examples, and references to aid study and research.
ncatlab.org
nLab is a collaborative wiki for advanced mathematics, with rigorous articles on topics like category theory, algebra, and topology. It includes representation theory and character theory articles, offering definitions, explanations, and literature references.