Complex sentence: Octagon were first incorporated in the US as Advantage International in April 1983; acquired by The Interpublic Group of Companies in 1997 and merged with several other IPG holdings, eventually being re-branded as Octagon in 1999 to be the Sports and Entertainment group of IPG.
Split into simpler sentences: Octagon were first incorporated in the US as Advantage International in April 1983; acquired by The Interpublic Group of Companies in 1997 and merged with several other IPG holdings. Eventually being re-branded as Octagon in 1999 to be the Sports and Entertainment group of IPG.