He should be a strong, experienced partner for the young head coach.
The Bears recently hired coach Matt Nagy, who has said he will handle the play-calling duties.
Helfrich led OR to a 37-16 record in four seasons.
Helfrich got his first major break in coaching joining Koetter's staff at Boise State in 1998 and then following Koetter to Arizona State.
Bears now have hired former Oregon HC Mark Helfrich as their offensive coordinator, per source. Line coach Harry Hiestand and running backs coach Charles London were hired on Wednesday. However, he finished 4-8 in 2016 and was dismissed.
Helfrich will not be calling plays initially, but he will inherit a second-year quarterback in Mitchell Trubisky.
They fired John Fox after three seasons with a 14-34 record that gave him the second-worst winning percentage for a Chicago coach.
Helfrich, 44, was the OR head coach from 2013-16, following four years of being the Ducks' quarterbacks coach-offensive coordinator under Chip Kelly.
The 39-year-old Nagy spent the past 10 seasons working under Andy Reid in Philadelphia and Kansas City. They Bears were 5-11 this past season.
The development of Trubisky, the No. 2 overall draft pick last spring, could go a long way toward lifting an offense that ranked 30th overall and last in passing.
The Bears were the first team to strike with their head coach and were able to put together a nice staff because of it. Tabor was Chicago's assistant special teams coach from 2008-2010.
Fangio has coached a total of 31 years in the National Football League, with additional stops in Baltimore, Houston, Indianapolis, Carolina and New Orleans.
It also signals the Bears' need to add speed and dynamic playmakers after the catch to an offense that was severely lacking in both areas, save for rookie sensation Tarik Cohen, whose upside is very exciting with the new creative offensive minds on board.