Why you think he a legend?
Because King and Urban Legends are both classics.
He went on a run from 2005 to 2008 that was up there with Lil Wayne and guys have no problem calling Wayne a legend. When very often T.I. has even had better verses than Wayne especially during that time frame
Often kills his features, has his own style and is basically the Jay Z of the South.
He didn't found trap music no...but he still was a heavy influence on the Young Jeezy and Guccis to follow what he did years prior.
He has had a HEAVY influence in the Atlanta Rap scene