Capella is the Silver Saint of the constellation of Auriga, the Charioteer.  He attacks by throwing saucers, which are actually more like discuses.  He and Cerberus Dante had been ordered to capture Kido Saori and take her to Sanctuary. 
 
When Phoenix Ikki appeared and warned the two not to fight him, Capella attacked immediately, and was stuck down almost instantly by Ikki's Phoenix Genma Ken (Illusion Fist).  He managed to get up and attack again, and he thought he had been successful, decapitating Ikki with a saucer, but the headless body kept advancing on him.  This was all part of the illusion, but the saucers Capella had thrown at the mirage returned, cutting off both his hands and smashing into his chest, finishing him off.