Appellant constituted a legitimate class of one, and this provides a basis for Congress's decision to proceed with dispatch with respect to his materials.

William J. Brennan, Jr.'s quote addresses a legal concept in which the appellant (the individual bringing the appeal) is recognized as a legitimate class of one. This means that, in this particular case, the appellant's situation is sufficiently unique or specific to merit individual consideration by the court. By describing the appellant as a "class of one," Brennan emphasizes the idea that the case should not be treated generically or as part of a larger group but should instead be handled based on its unique circumstances.

The phrase "provides a basis for Congress's decision to proceed with dispatch" refers to the importance of this individual case in influencing how Congress or the courts move forward with handling matters related to the appellant's materials or situation. This suggests that the urgency or priority of the case has been established, and therefore, it justifies swift action. Brennan is indicating that the legal process should proceed quickly in light of the appellant’s specific claim.

This quote likely originates from a court opinion written by Brennan, known for his strong advocacy for individual rights and his willingness to assert the importance of unique cases when interpreting the Constitution. His use of the "class of one" argument often appears in cases where someone’s rights or legal standing cannot be easily generalized to others, requiring distinct legal treatment.

In broader legal terms, the class of one concept has been applied in cases where an individual asserts that they have been treated differently or unfairly compared to others under the law. Brennan’s comment would likely be part of a broader judicial analysis examining whether the appellant’s case warranted specific consideration and action based on its individual merits, which in turn could influence legislative or judicial decision-making.