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A longtime D.E. Shaw portfolio manager says he was unfairly terminated after an investigation into allegations of inappropriate behavior. Now he's fighting back.

D.E. Shaw fired Daniel Michalow, a senior portfolio manager in the firm's discretionary macro group, after the $50 billion fund conducted an investigation into the high-profile portfolio manager in March. The investigation was sparked after Michalow allegedly said to a former assistant that one of the requirements for hiring a new assistant was someone that he could "call sugar tits," people familiar with the matter told Business Insider.

The firm's human-resources department launched a formal investigation during which several women came forward with complaints about his behavior, the people said. Michalow was then temporarily suspended before his firing.

Michalow wrote a five-page letter to firm founder David Shaw on May 7 that was obtained by Business Insider. Michalow confirmed to Business Insider by email that he had sent the letter to Shaw, but declined to comment further on his departure from the firm.

Here's our story. And here's the memo D.E. Shaw sent to employees in the fallout from the firing.

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