The definitive California case is: La Sala v. American Sav. & Loan Assn., 5 Cal. 3d 864, 871 (1971). It holds (relevant on both the question of fiduciary duty and individual settlement):
"When a plaintiff sues on behalf of a class, he assumes a fiduciary obligation to the members of the class, surrendering any right to compromise the group action in return for an individual gain. Even if the named plaintiff receives all the benefits that he seeks in the complaint, such success does not divest him of the duty to continue the action for the benefit of others similarly situated."
California law for derivative securities cases is similar:
"He sues, not for himself alone, but as representative of a class comprising all who are similarly situated. The interests of all in the redress of the wrongs are taken into his hands, dependent upon his diligence, wisdom and integrity. . . . He is a self-chosen representative and a volunteer champion. . . . One who assumes such a fiduciary role cannot abandon it for personal aggrandizement."
Heckmann v. Ahmanson, 168 Cal. App. 3d 119, 129 (1985)