St. George by Donatello is a classic example of the early renaissance - the return of the human figure, "rendered as a self-activating, functional organism... shown with a confidence in its own worth(1)". St. George is shown as the clear eyed vanquisher of the dragon, calmly and confidently assuming his pose. Their are several marble copies of this sculpture - including the current one in the niche, as well as a bronze. The original now appears to be in the Orsanmichele museum - but at one point (when it was first removed from the church in 1892) was placed in the Bargello, as was the predella (the predella at Orsanmichele is a copy - the only copy of all the tabernacles and predellas as far as I have learned).
This sculpture was commissioned by the Armorer's and Sword Makers Guild and completed c. 1417-18. It is on the north side of the church on Via Orsamichele. Though the tabernacle was also done by Donatello it lacks any renaissance style and is much more in line with some of the other gothic tabernacles of the church. The statue probably once also had a sword or spear in George's right hand, as well as a helmet. When these were lost is not well documented.