The guitarist and singer was known in musical circles as the Professor.
The Welsh-born musician, who produced hits including Keep On Running and I’m A Man, died in hospital while being treated for pneumonia.
His agent Bob Birk told the PA news agency: “I have represented him as his agent for over 30 years.
He was a highly ethical, very talented, good hearted, extremely intelligent, generous man
Bob Birk, Spencer Davis's agent
“He was a very good friend. He was a highly ethical, very talented, good hearted, extremely intelligent, generous man.
“He leaves behind his long-time domestic partner June and three adult children.
“He will be missed.”
Davis, who was known in musical circles as the Professor, was born in Swansea and began learning harmonica and accordion at the age of six.
In 1960, he moved to Birmingham to read German at the University of Birmingham, where he was further exposed to burgeoning genres such as skiffle, jazz, and blues.
He formed The Spencer Davis Group in 1963, featuring Steve Winwood on keyboards and guitar, his brother Muff Winwood on bass, and Pete York on drums.
They originally performed as the Rhythm and Blues Quartet and played mostly R&B covers.
Within a year, they had landed a regular gig at the famous Marquee Club on Oxford Street in London, and by 1964 had adopted the name The Spencer Davis Group.
They topped the UK singles chart twice and had seven top 40 singles, according to the Official Charts Company.
The original line-up were together for six years, with subsequent reunions featuring a variety of new players.
The track Gimme Some Lovin’ famously featured on the soundtracks of films The Blues Brothers and Notting Hill.
Music by The Spencer Davis Group is also included in the recent Helen Reddy biopic I Am Woman.
Actor Philip Martin Brown was among those paying tribute.
He said on Twitter: “#RIP Spencer Davis. Such happy memories of Northern Soul dancing to This Hammer.”
The Brian Jonestown Massacre frontman Anton Newcombe shared a video of the band performing Gimme Some Lovin’.
He wrote: “Rest In Peace Spencer Davis.”
Horace Panter, bassist with ska band The Specials, tweeted: “One of the pioneers of those great 60s bands fusing soul and R&B into rock. Remember first hearing #thespencerdavisband as an impressionable teenager. Just got their album out so turntable beckons.”
Stevie Van Zandt, best known as a member of Bruce Springsteen’s E Street Band, said he was a fan of Davis, tweeting: “The British Invasion is my main thing. RIP Spencer Davis. Thank you.”