TIEING THE KNOT: U.S. drugmaker Perrigo agreed Monday to buy Ireland's Elan for $8.6 billion in a deal that should allow the rapidly growing company to reduce its tax bill and boost its royalty stream.

HOT TARGET: Elan was pursued by several U.S. companies, including hostile bidder Royal Pharma, who sought to acquire Elan's flow of royalties from drugs it helped develop, particularly the multiple sclerosis fighter Tysabri.

BOOM, BUST AND RECOVERY: Elan soared in the late 1990s as it positioned itself as a biotechnology pioneer, but it faced ruin in 2002 after its Alzheimer's trials failed and the company was caught hiding losses in Enron-style accounting tricks. A new management team then drastically pared down Elan and focused on developing Tysabri.