After years of effort, he finally realized his dream of starting his own company.

realized 是动词 realize 的过去式。realize 由词根 real（真实的）和后缀 -ize（使...化）组成，字面意思是"使...成为现实"，引申为"实现、认识到"的意思。在句中表示"使梦想成为现实"这一动作已经完成。