David Moyes said it is "great to be back" after being appointed Everton manager for a second time.
The 61-year-old Scot has signed a two-and-a-half-year contract at Goodison Park following the sacking of Sean Dyche on Thursday.
Everton are 16th in the Premier League - one point clear of the relegation zone - with only three wins from 19 games this season.
"I enjoyed 11 wonderful and successful years at Everton and didn't hesitate when I was offered the opportunity to rejoin this great club," said Moyes.
"Now we need Goodison and all Evertonians to play their part in getting behind the players in this important season so we can move into our fabulous new stadium as a Premier League team."
Moyes managed Everton from 2002 until 2013 before spells in charge of Manchester United, Real Sociedad, Sunderland and West Ham twice.
He has been out of work since leaving West Ham, where he won the Europa Conference League in 2023, at the end of last season.
Moyes spent 11 years at Everton before leaving to take charge of United as Sir Alex Ferguson's successor in the summer of 2013.
Following a four-year spell at Preston, he joined Everton in March 2002, with the Toffees in danger of relegation.
Moyes won his first match and went on to take charge of more than 500 games.
Everton reached the FA Cup final in 2009 and finished in the top eight of the Premier League nine times, including fourth in 2004-05, which took them into Champions League qualifying.
Moyes gave Wayne Rooney his professional debut and signed several players who would become Everton greats, including Tim Cahill and Marouane Fellaini.
Moyes was handpicked by Sir Alex as his successor at Old Trafford but failed to see out the 2013-14 season.
He was sacked in April 2014 after 10 months in charge, with United seventh in the table and unable to qualify for the Champions League.
Moyes had a year in La Liga with Sociedad before returning to English football with Sunderland, who were relegated from the Premier League in 2016-17.
Moyes helped West Ham avoid relegation in 2017-18 during a six-month spell in charge.
He was close to signing a deal to succeed Marco Silva at Everton in December 2019, but owner Farhad Moshiri appointed Carlo Ancelotti.
Moyes returned to West Ham that month following the sacking of Manuel Pellegrini, and remained in charge until the end of the 2023-24 season.
In that time he led them to two top-seven finishes and won the Europa Conference League, their first major trophy for 43 years.
Everton's numbers in the league this season make for grim reading:
Only in three seasons in their history have they scored fewer goals after 19 games.
They have the division's lowest expected goals (xG) at 18.33.
Their tally of 63 shots on target is the second lowest behind Southampton's 58.
Everton's average of 0.79 goals per game is their lowest in 13 seasons. It was 1.05 last season and 0.89 in 2022-23.
Shamoon Hafez, BBC Sport football news reporter
With Everton teetering above the drop zone, Moyes' key task will be to ensure the club move into their new stadium on Bramley-Moore Dock next season playing Premier League football.
The side have been sound defensively but stagnated under Dyche's one-dimensional style of play, with the team creating few chances and the goals drying up.
Strikers Dominic Calvert-Lewin and Beto have struggled to score through a lack of service, but will now have a fresh start under a new boss with different ideas to help fire the club back up the table.
Supporters had grown tired of watching the team and, despite a general consensus that dismissing Dyche was the correct decision, there was a subdued atmosphere in the FA Cup third-round tie against Peterborough on Thursday evening.
The Blues faithful have been starved of success, but a significant issue at the club in recent years has been a lack of stability.
The Toffees have had to install yet another man in the dugout, and caretaker boss Leighton Baines said there has to be "hope and optimism" amid the managerial change.
Moyes is a safe pair of hands as he returns to familiar surroundings, with the hierarchy bringing back someone who many fans wanted. Their job now is to stand by the new manager.