Wales captain Alun Wyn Jones will lead the 2021 British & Irish Lions on their tour of South Africa this summer with England's Kyle Sinckler and Ireland skipper Johnny Sexton missing out on the 37-man squad.
Gatland's squad included surprise picks Bundee Aki (Ireland) and Jonny Hill (England), but there was no place for Sexton, nor England tight-head Sinckler.
Manu Tuilagi was also rumoured to be in the mix for selection but misses out, while there is also no place for Cian Healy (Ireland), James Ryan (Ireland), Billy Vunipola (England) or Jonathan Davies (Wales).
The Lions looked set to pick a 36-man squad, but included one extra player following a four-hour selection meeting on Wednesday. The split sees 10 Wales players included, 11 from England, eight from Scotland and eight from Ireland.
"We believe we've picked a squad capable of winning a Test series in South Africa," Gatland said. "Selecting a Lions squad is never easy and, in many ways, this has been the most challenging selection I have been involved in. Over the course of the last three weeks the coaches and I have rigorously debated each position.
"We saw some outstanding performances in the recent Six Nations, so competition for places has been tough with some incredibly tight calls to make. However, we are very happy with the squad we have assembled and look forward to meeting up in Jersey in just over a month's time to start our preparation to take on the World Champions.
"We've left out some very talented players which gives an indication to the strength of this squad and we know how important that stand-by list will be. Being selected for a Lions Tour is the greatest honour for a British and Irish player and I congratulate everyone named today."
The backs see Liam Williams and Stuart Hogg named as fullbacks, with Josh Adams, Louis Rees-Zammit, Anthony Watson and Duhan van der Merwe the options on the wing. Aki, Chris Harris, Robbie Henshaw, Elliot Daly are named as centres, while Owen Farrell, Dan Biggar and Finn Russell are the fly-halves. Gareth Davies, Conor Murray and Ali Price are the three scrum-halves.
In the pack, Gatland has opted for three loose-heads in Mako Vunipola, Rory Sutherland and Wyn Jones, while Andrew Porter, Zach Fagerson and Tadhg Furlong head on tour as the three tight-heads. Ken Owens, Jamie George and Luke Cowan-Dickie are the trio of hookers.
Gatland has opted against picking an out-and-out blindside flanker, with hybrids the favoured option. Maro Itoje and Tadhg Beirne head as versatile forwards, while captain Jones is joined in the second-row alongside England's Hill and Courtney Lawes, and Ireland's Iain Henderson. And in the back-row, Jack Conan, Taulupe Faletau, Hamish Watson, Justin Tipuric, Sam Simmonds and Tom Curry all head.
Captain Jones, 35, holds the record for the most caps in men's international rugby, and is regarded as one of the great second rows.
The hugely experienced lock will join forces with his old Wales boss Gatland as they aim to win the Lions' first Test series against the Springboks since 1997.
This will be Jones' fourth tour with the Lions having journeyed to South Africa in 2009, Australia in 2013 and New Zealand in 2017. He has won nine Lions Test caps to date and captained the side in the third Test against the Wallabies in 2013.
Jones has just skippered Wales to the 2021 Six Nations, and has been picked ahead of other contenders Itoje, Farrell and Hogg.
"I'm obviously very proud and privileged," Jones said. "To be selected in the squad is initially what you want to be hearing as a player. To have the armband as well is a privilege.
"I had a call from Gats on Sunday evening -- actually a missed call. I thought I'd better give him a call back. We had a quick chat and I accepted obviously.
"Initially the draw is to get into the squad. I've just got a huge amount of pride to be able to add this to the CV."
While Gatland has previously emphasised that tour captaincy does not guarantee Test selection, Jones will be charged with heading up the leadership group as the Lions embark on this eight-match tour in South Africa, including the three Tests against the reigning World Cup champions.
The Lions' schedule starts with a game against Japan at Murrayfield on June 26. They then travel to South Africa where their stay will be split between Johannesburg and Cape Town, due to scheduling challenges because of COVID-19 restrictions.
The team will open their South Africa programme against the Stormers on July 3 and then face a South Africa Invitation XV, the Sharks, South Africa A and the Bulls before playing the Springboks on July 24 in Johannesburg.
Then the Lions will journey back to Cape Town for the second Test, before finishing up in Johannesburg for the final Test against South Africa on Aug. 7.
Backs: Josh Adams (Wales), Bundee Aki (Ireland), Dan Biggar (Wales), Elliot Daly (England), Gareth Davies (Wales), Owen Farrell (England), Chris Harris (Scotland), Robbie Henshaw (Ireland), Stuart Hogg (Scotland), Conor Murray (Ireland), Ali Price (Scotland), Louis Rees-Zammit (Wales), Finn Russell (Scotland), Duhan van der Merwe (Scotland), Anthony Watson (England), Liam Williams (Wales).
Forwards: Tadhg Beirne (Ireland), Jack Conan (Ireland), Luke Cowan Dickie (England), Tom Curry (England), Zander Fagerson (Scotland), Taulupe Faletau (Wales), Tadhg Furlong (Ireland), Jamie George (England), Iain Henderson (Ireland), Jonny Hill (England), Maro Itoje (England), Alun Wyn Jones (captain, Wales), Wyn Jones (Wales), Courtney Lawes (England), Ken Owens (Wales), Andrew Porter (Ireland), Sam Simmonds (England), Rory Sutherland (Scotland), Justin Tipuric (Wales), Mako Vunipola (England), Hamish Watson (Scotland).