Vasilis Barkas set his sights on helping Celtic to 10-in-a-row after joining the Scottish champions on a four-year deal from AEK Athens.
The 26-year-old goalkeeper, who has been capped 10 times by Greece, has spent the past four years with AEK.
Boss Neil Lennon had been looking for a goalkeeper following the return of Fraser Forster to Southampton and the departure of Craig Gordon.
Celtic begin their quest for a 10th successive Premiership title with a home game against Hamilton on Sunday.
Barkas told Celtic TV: "I'm very happy to be here, it's a dream to come to one of the biggest teams in Europe, and I can't wait to play for Celtic.
"Winning medals and trophies is why I came here.
"I want to win 10 in-a-row, and I want to help us get into the Champions League. That's what I want.
"The manager spoke to me about the club, the pressure here and that he wants us to be champions again.
"That's one of the reasons I came here, and I think that him and I have a very good relationship so far."
Barkas has already played at Celtic Park when AEK took on the Scottish champions in the third qualifying round of the Champions League in 2018.
He becomes Celtic's second Greek player, following in the footsteps of Georgios Samaras, who spent five-and-a-half-years with the Hoops, making 253 appearances and scoring 74 goals.
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