Highlander II: The Quickening

Professor Allan Neyman and Connor MacLeod create a shield to save Earth from ozone damage in 1999. However, 25 years later, the shield's unintended effects are killing the planet. A terrorist group led by Louise Marcus seeks to destroy the shield. The story flashes back to reveal MacLeod and his friend Juan Sánchez Villa-Lobos Ramírez, two aliens from the planet Zeist, who were banished by the tyrant Katan.