Bill Gross, the bond market’s most renowned investor, quit Pimco for distant rival Janus Capital Group Inc on Friday, the day before he was expected to be fired from the huge investment firm he co-founded more than 40 years ago. Gross, 70, had been clashing with the firm’s executive committee and had threatened to resign multiple times, a source familiar with the situation said. The committee had planned to accept his latest resignation from the post of chief investment officer on Saturday.