Dr. Kjell Norwood Lindgren (born January 23, 1973) is a current NASA astronaut.
 Lindgren was selected in June 2009 as a member of the NASA Astronaut Group 20.
 He launched to the International Space Station (ISS) as part of Expedition 44/45 on July 22, 2015.
Koichi Wakata (若田 光一 , Wakata Kōichi , born 1 August 1963) is a Japanese engineer and a JAXA astronaut.
 Wakata is a veteran of four NASA Space Shuttle missions, a Russian Soyuz mission and a long-duration stay on the International Space Station.
 During a nearly two decade career in spaceflight he has logged more than eleven months in space.
 During Expedition 39, he became the first Japanese commander of the International Space Station.
 Wakata flew on the Soyuz TMA-11M/Expedition 38/Expedition 39 long duration spaceflight, from 7 November 2013 to 13 May 2014.
 During this spaceflight he was accompanied by Kirobo, the first humanoid robot astronaut.
Oleg Dmitriyevich Kononenko (Russian: Олег Дмитриевич Кононенко ) is a Russian cosmonaut.
 He has flown to the International Space Station three times, as a flight engineer for Expedition 17 aboard Soyuz TMA-12, as a flight engineer on Expedition 30 and commander of Expedition 31 aboard Soyuz TMA-03M, and as a flight engineer on Expedition 44 and Expedition 45 aboard Soyuz TMA-17M.
 Kononenko has accumulated over 533 days in orbit during three long duration flights to ISS.
Peggy Annette Whitson (born February 9, 1960) is an American biochemistry researcher, NASA astronaut, and former NASA Chief Astronaut.
 Her first space mission was in 2002, with an extended stay aboard the International Space Station as a member of Expedition 5.
 Her second mission launched October 10, 2007, as the first woman commander of the ISS with Expedition 16.
 She was currently in space on her third long-duration space flight and was the commander of the International Space Station for Expedition 51, before handing over command to Fyodor Yurchikhin on June 1, 2017.
The International Space Station program is tied together by a complex set of legal, political and financial agreements between the fifteen nations involved in the project, governing ownership of the various components, rights to crewing and utilization, and responsibilities for crew rotation and station resupply.
 These agreements tie together the five space agencies and their respective International Space Station Programs and govern how they interact with each other on a daily basis to maintain station operations, from traffic control of spacecraft to and from the station, to utilization of space and crew time.
 In spring 2010, the International Space Station Program Managers from each of the five partner agencies were presented with Aviation Week's Laureate Award in the Space category, and NASA's International Space Station Program was awarded the 2009 Collier Trophy.
Expedition 45 was the 45th expedition to the International Space Station.
 Scott Kelly and Mikhail Korniyenko transferred from Expedition 44 as part of their year-long stay aboard the ISS.
 Expedition 45 began with the arrival of Soyuz TMA-18M at the ISS on September 11, 2015, and concluded with the departure of Soyuz TMA-17M on December 11 2015.
 Kelly, Korniyenko and Sergey Volkov then transferred to the crew of Expedition 46.
Scott Joseph Kelly (born February 21, 1964 in Orange, New Jersey) is an engineer, retired American astronaut, and a retired U.S. Navy Captain.
 A veteran of four space flights, Kelly commanded the International Space Station (ISS) on Expeditions 26, 45, and 46.
Soyuz TMA-17M was a 2015 flight to the International Space Station.
 It transported three members of the Expedition 44 crew to the International Space Station.
 TMA-17M was the 126th flight of a Soyuz spacecraft; the first having occurred in 1967.
 The crew consisted of a Russian commander accompanied by Japanese and American astronauts.
 The capsule remained docked to the space station for about five months until the scheduled departure of Expedition 45 in December 2015.
 Soyuz TMA-17M landed safely on the steppes of Kazakhstan on 11 December, 2015, in a rare night landing.
Soyuz TMA-19 was a manned spaceflight to the International Space Station and is part of the Soyuz programme.
 It was launched June 15, 2010 carrying three members of the Expedition 24 crew to the International Space Station, who remained aboard the station for around six months.
 TMA-19 was the 106th manned flight of a Soyuz spacecraft, since the first mission which was launched in 1967.
 The spacecraft remained docked to the space station for the remainder of Expedition 24, and for Expedition 25, to serve as an emergency escape vehicle.
 It undocked from ISS and landed in Kazakhstan on the November 26, 2010.
 It was the 100th mission to be conducted as part of the International Space Station programme since assembly began in 1998.
Joseph Michael "Joe" Acaba (born May 17, 1967) is an educator, hydrogeologist, and NASA astronaut.
 In May 2004 he became the first person of Puerto Rican heritage to be named as a NASA astronaut candidate, when he was selected as a member of NASA Astronaut Training Group 19.
 He completed his training on February 10, 2006 and was assigned to STS-119, which flew from March 15 to March 28, 2009 to deliver the final set of solar arrays to the International Space Station.
 Acaba served as a Flight Engineer aboard the International Space Station, having launched on May 15, 2012.
 He arrived at the space station on May 17 and returned to Earth on September 17, 2012 at 6:53am Moscow Standard Time when touchdown was officially recorded by the Russian Federal Space Agency.
 Acaba returned to the International Space Station in 2017 as a member of Expedition 53/54.

Question: Who was the retired American astronaut who transferred from Expedition 44 to 45 on the International Space Station?
Answer: Scott Kelly