In the 2003 “merger of equals” that created Biogen Idec, Idec was the acquiring company and surviving legal entity even though the management team and the headquarters operation in Cambridge, MA came entirely from Biogen. Idec was made the surviving legal entity to circumvent a change-of-control provision in Idec’s Rituxan partnership with Genentech/Roche. (Idec’s shareholders ended up with slightly more than 50% of the equity in the merged company.)
By now, Idec’s legacy is hard to find in BIIB’s drug portfolio and pipeline, so the name simplification makes sense.