They may also be seen in family gatherings, such as Barney and Robin's wedding or Marshall's father's funeral. Eriksen (son of Marshall and Lily) appear in the background of many episodes without being crucial to many plots.
Ranjit, Carl the Bartender, and several other characters often appear because they work in places the main cast frequent (such as Mac Laren's Pub).
Robin was named after her father, who she has some issues with as he wanted a male child.
She and Ted have an on-again, off-again relationship there was some sexual tension between them throughout the third season, most obviously when Robin brought home her boyfriend Gael from a trip to Argentina.
Ted finally gets to meet his wife-to-be, Tracy, on the day of Barney and Robin's wedding, after accidentally teaching one of her college classes, owning her yellow umbrella for a short time, and dating her roommate.
When he ran into Tracy's roommate (Cindy), it led to Tracy's band performing at Barney and Robin's wedding.
A brief history of Ted includes being left at the altar, taking a job as an architecture professor and designing the new headquarters for Goliath National Bank.