What is the name of a "role" in a family tree? / What is the name of the initial person in a family tree?

I have two questions concerning family trees:

1. What is the name of the initial person in a family tree? For example, if you want to know the family tree of a certain person, you have that person in the center and then draw lines from that person referring to all of that person's relatives, ancenstors, descendants, partner and siblings. Is it called individual?
2. What is the name of the role a certain person has in a family tree? For example a sister, mother, father, aunt, etc?

Solution 1:

Of course, sources may differ in the terminology they prefer. Sometimes subject is used for the person whose family tree is being developed, and relationship is used for all of the positions (parents, siblings, aunts, uncles, cousins, etc.) to specify how the people are related to one another.

http://www.eogen.com/Relationships

Solution 2:

The term is progenitor.

A progenitor is a person or thing from which others are descended or originate. For example, it is used to refer to the ancestor who started the line of a noble family.

In a wider sense today it is used to refer to the person who originates a movement or way of life.

Read more at Wikipedia.