Can anyone build a fund management brand to rival Fidelity Investments’? Ellyn McColgan, 53, who helped build the Boston giant’s brand during a 17-year career that ended abruptly last August, would sure like to try. That’s one reason she accepted an offer to succeed James Gorman, chief operating officer of Morgan Stanley Global Wealth Management, when he was promoted in December to co-president of the parent company. “What she brings to the table is truly additive — a long track record of running and building a business and a great brand,” says Gorman. McColgan starts her new job in April.