A “fallen angel” is a company or an investment that formerly had been successful, but has fallen in value. Investing in “fallen angels” is risky—a company could go back up in value or it could go bankrupt.
 
The financial term “fallen angel” has been cited in print since at least March 1982.
 
         
Wikipedia: Fallen angel
A fallen angel, in Christian mythology, is an angel who has been exiled or banished from Heaven. Often such banishment is a punishment for disobeying or rebelling against God (see War in Heaven).
 
The best-known fallen angel is Lucifer, a name frequently attributed to Satan in Christian belief. This usage stems from a particular interpretation of Isaiah 14:3-20 that speaks of someone who is given the name of “Day Star” or “Morning Star” (in Latin, Lucifer) as fallen from heaven. The word Lucifer, however, does not refer to Satan anywhere in the Bible. Some see the passage as using this name to describe the king of Babylon, who had exalted himself as being deity himself, after which God would cast him down. The same terminology is used in Ezekiel to describe the king of Tyre. The Greek etymological synonym of Lucifer, Eωσφόρος (Eosphoros, “dawn-bearer”) is used of the morning star in 2 Peter 1:19 and elsewhere with no reference to Satan.
 
Investopedia
What Does Fallen Angel Mean?
1. A bond that was once investment grade but has since been reduced to junk bond status.
2. A stock that has fallen substantially from its all time highs.
 
The Free Dictionary
fallen angel
A once-popular security that has lost investor favor and has declined in value. For example, a high-growth company may hit a period of heavy competition or saturated markets such that its stock declines in price and becomes a fallen angel.
 
The Free Dictionary
a fallen angel
a company or sports team that was successful in the past but is not successful now (usually plural) Derby County were this season’s fallen angels, being sent into the Second Division after losing all their matches.
 
Google News Archive
28 March 1982, Youngstown (OH) Vindicator, “Jimmy Rogers Is Alive, Well, and Still Making Millions” by Dan Dorfman, pg. B15, col. 1:
If you’re interested in a stock group brimming with candidates that could double in price over the next three years (utilities), a fallen angel that can rebound as a new market star (Tampax), a super short sale or a stock you’re betting will go lower (CBS), or in how to make upward of 100 percent on a fixed-income instrument (Public Housing Authority municipal bonds), you might want to give a fella I know a fair hearing.
 
Google Books
Street Smart Investing:
A price and value approach to stock market profits
By George B. Clairmont and Kiril Sokoloff
New York, NY: Random House
1983
Pg. 118:
Collecting “Fallen Angels”
     
26 June 1983, New York (NY) Times, “Some say the big money has been made and Wall Street may have to make do with smaller gains” by Leslie Wayne, pg. F27:
“There’s hardly a major stock that hasn’t had a correction over the past nine months,” said Stefan Abrams, a managing director at Oppenheimer & Company. “The averages don’t feel this. But, if you bought Texas Instruments or Warner Communications or any of the fallen angels, you will have lost real money.”
 
7 August 1983, New York (NY) Times, “How to Spot the Turnaround Stocks” by Eric N. Berg, pg. F17:
“It’s a high-risk game but an extremely rewarding one if you are right,” said Martin D. Sass, president and chief executive of the M. S. Sass Investors Services Company, a Wall Street firm that invests in “fallen angels”—blue-chips experiencing temporary financial distress. “It’s hazardous, but I know many people who make a business out of it successfully.”
 
1 September 1985, New York (NY) Times, “Investing” by Anise C. Wallace, “Fallen Angels and Kickers,” pg. F8:
Mr. Solomon concedes that there is risk in the junk market, especially with some of the issues financing leveraged buyouts. But lately he has been buying issues of the “fallen angels,” including steel companies such as LTV Corporation.
 
OCLC WorldCat record
High steppers, fallen angels, and lollipops : Wall Street slang
Author: Kathleen Odean
Publisher: New York : Dodd, Mead, ©1988.
Edition/Format:  Book : English : 1st ed