Over the weekend, the Church commemorated two saints, one vastly more popular than the other. St. Nicholas, Bishop of Myra (in modern-day Turkey), is known for many things. He was a survivor of the Diocletian persecution of the Church. He attended the Council of Nicaea in 325 A.D.; this council created the original Nicene Creed. In his day, he was well-known as a lover of the sea and a protector of sailors, leading to his designation as the patron saint of sailors as well as many congregations in port cities naming their churches after St. Nicholas. But St. Nicholas is most-well known as someone who protected children and gave many gifts to the poor. These traits of his led to him being the inspiration for Santa Claus. You can read more about these stories here.
St. Ambrose is not as well-known today, but was a key theologian in the early church. He wrote extensively and was highly regarded as a preacher and orator. St. Augustine gave credit to St. Ambrose for convincing Augustine to convert to Christianity. St. Ambrose fought against early heresies within the church and used his extensive knowledge of the Greek language to influence the development of the early Church's theology. A more extensive telling of his work can be found here.
The Church commemorated St. Nicholas on December 6th and St. Ambrose on December 7th.