Which NASA astronaut logged eight spacewalks and flew on three Hubble servicing missions? The answer is John Grunsfeld.
John M. Grunsfeld is a physicist and former NASA astronaut who flew on five Space Shuttle missions. Three of them—STS-103 in 1999, STS-109 in 2002, and STS-125 in 2009—serviced or upgraded the Hubble Space Telescope. Across those missions, he performed eight spacewalks totaling 58 hours and 30 minutes.
His work included installing new instruments, replacing gyroscopes and batteries, fitting new solar arrays, and helping add the Advanced Camera for Surveys, the Power Control Unit, and the Wide Field Camera 3. On STS-109, he served as payload commander and led the spacewalking activities.
The other names are associated with Hubble too. Steven Smith flew on servicing missions, Michael Massimino performed Hubble spacewalks, and Andrew Feustel worked on Hubble during STS-125, but none matches the complete combination of three servicing missions and eight total spacewalks.