I am reading the paper Chern-Weil map for principal bundles over groupoids. In page number $13$, authors say

let us recall the definition of fundamental group of a topological groupoid.

But, they do not give any reference (or I could not see where they have given reference) for original paper, where the notion of fundamental group of topological/Lie groupoid is introduced.

Can some one point me to some reference where this has been mentioned for the first time?

Side question : Do we have notion of fundamental group for ``other kinds" of algebraic/differential geometrical objects? Do we have fundamental group of, say, an algebraic variety, or a scheme or similar such thing?