Complex sentence: Between 1996 and the summer of 2002, Ireland's main shirt sponsor was Irish Permanent who became Permanent TSB after a merger, who continued to sponsor the shirt until the autumn of 2006.
Split into simpler sentences: Between 1996 and the summer of 2002, Ireland's main shirt sponsor was Irish Permanent. They were replaced by Permanent TSB, who sponsored the shirt until the autumn of 2006.