How Allergan went from a tiny Los Angeles eye care company to one of the biggest takeover targets of 2015

Last week, Allergan Plc, a drugmaker known for its best-seller Botox, said it is in the beginning stages of talks to merge with pharmaceutical giant Pfizer Inc.

The company, which was recently created as a combination of Actavis Plc and Allergan, is the obvious acquisition target for Pfizer, if only because it would help cut the drug giant's tax bill. Pfizer is known for making blockbuster drugs Viagra and Lipitor.

Here's the story of how Allergan went from a small Los Angeles company known for making eye-drops to an Ireland-domiciled drug giant with a market value of $123 billion, and potentially 2015's biggest takeover target.