Dr. Cross

Dr. Cross is one of the main characters of Polygoons. He is a beige cross sign.

Character
He is a super-smart and well-meaning scientist and inventor. He is usually a friend to the Polygoons. Triangle Man's antics often ruin his inventions. His superior intellect sometimes aggravates Mr. Pentagon.

Debut
He was created by a fan, Brielle Duukovicc, as the winning entry for a fanart event called the "Create-a-Goon Contest". The contest was held by the official Polygoons Instagram account, and the winner got their character added to the main cast of the comic. He made his first comic appearance in "Polygoons #28" and has become a recurring character since then.

Square Guy
Square guy seems to be more of a normal patient than an actual friend. Dr. Cross was the one who told Square guy he was color blind and the one to tell him Triangle Man had an incurable virus.

Triangle Man
They have interacted once in comic but Triangle man was mentioned once by Dr. Cross in comic #49 meaning the two have interacted at least one other time. Dr. Cross probably sees Triangle Man as just another patient

Heather Hexagon
They have yet to interact

Mr. Percy Pentagon
The two seem like friends but fight in a battle of wits.

Dave Diamond
The two have not talked directly but Dave has been seen in the same comic as Dr. Cross.

Carol
Carol took the kids.