Aleksei Alexeyevich Oleinik (born June 25, 1977, as Oleksíy Oleksíyovych Olíynyk) is a Russian[3][2] mixed martial artist and combat sambo fighter who fought for the Ultimate Fighting Championship, competing in their heavyweight division.

[13] Oleinik made his return to grappling in a superfight against multiple-time World Champion Gordon Ryan on December 12, 2019 at Quintet: Ultra.

Then, it turned out that I do it very well, and became my profession.”[16] Oleinik represented Russia for the Imperial Team in the M-1 Challenge 2009 season, where he defeated Sang Soo Lee.

Alexey has highly regarded submission grappling skills which he developed from his background in training in traditional Japanese jujutsu[17][18][19] and competition in Combat Sambo.

He fought Robin Gracie trained Spanish BJJ black belt Rogent Lloret in a fight that ended in a draw.

That streak came to a halt when he lost via TKO in the first round against Michal Kita at the ProFC Heavyweight Grand Prix 2009.

In the summer of 2010, under the tutelage of K-Dojo Head Coach Murat Keshtov, Oleinik participated in the inaugural heavyweight tournament for Bellator Fighting Championships.

[22] In his debut, Oleinik faced fellow newcomer Anthony Hamilton on June 28, 2014, at UFC Fight Night: Swanson vs.

[26] In an interview on September 9, 2015, Oleinik indicated that he had been sidelined by multiple knee surgeries and subsequent rehabilitation.

[30] He won the fight in the first round via Ezekiel choke, the first in UFC history and was awarded a Performance of the Night bonus.

[36] The referee stopped the fight in the second round after Blaydes delivered an illegal kick to a downed opponent and called a doctor to check on Oleinik.

The replay, however, showed the strike did not deliver significant damage (as it only grazed the ear), and the fight was ruled a TKO win for Blaydes.

[40] Oleinik was briefly linked to a bout with Fabrício Werdum on September 15, 2018, at UFC Fight Night 136.

[48] Oleinik faced Alistair Overeem on 20 April 2019 at UFC Fight Night 149, replacing Alexander Volkov.

[60] When he announced he was taking another fight, Oleinik "received a message in a bottle" on the beach of Miami, signed his contract, and sent it back to Dana White and Mick Maynard.

[61] When asked if Oleinik planned on retiring any time soon, he jokingly responded that he has "only 10 years left.

[69] Oleinik was scheduled to face Ilir Latifi on March 26, 2022, at UFC Fight Night 205.

[81] He is a naturalised Russian citizen,[82] and expressed support towards Russia following its 2014 military intervention in Ukraine.