Question: Which singer is also a guitarist, Kang Seung-yoon or Piotr Wiwczarek?

Documents:
source: Kang Seung-yoon
text: Kang Seung-yoon Kang Seung-yoon (born (1994--) 21, 1994 ), known as Seungyoon, is a South Korean singer-songwriter, record producer, actor, and leader of boy group Winner. In 2010, he participated in the reality television singing contest "Superstar K2" and finished in fourth place. In January 2011, he became a trainee under YG Entertainment and went on to debut as a solo artist in July 2013 and as the leader of Winner in October 2013.

source: Piotr Wiwczarek
text: Piotr Wiwczarek Piotr Wiwczarek (born 22 October 1965 in Olsztyn, Poland), also known as Peter, (ex nickname Behemoth) is a Polish guitarist and vocalist who is the frontman for the death metal band Vader, as the only constant member of the band since its inception. He has also collaborated with Kazimierz "Para" Paraszczuk on his tribute album, Bandid Rockin', and is the producer of several of Vader's releases. He is also the founder and guitarist of a side-project, named Panzer X.

source: Vader discography
text: Vader discography The discography of Vader, a Polish death metal band, consists of ten studio albums, two compilation albums, two live albums, eight extended plays, one cover album, four video albums, nine singles, twelve music videos, and three demo albums. Formed in 1983, the group was founded by then bassist Piotr "Peter" Wiwczarek, and guitarist Zbigniew "Vika" Wróblewski.

source: Winds of Creation
text: Winds of Creation Winds of Creation is the debut studio album by Polish death metal band Decapitated. It was released through Earache Records subsidiary Wicked World on 11 April 2000. The album was produced by Piotr Wiwczarek (aka Peter), from Polish death metal band Vader.

source: Love for a Thousand More
text: Love for a Thousand More Love for a Thousand More (Hangul: 천년째 연애중 ; Hanja: 千年恋爱中 ; RR: "cheonnyeonjjae yeon-aejung " ) is a South Korea web series starring Kang Seung-yoon and . The drama is aired every Monday, Wednesday and Friday at 11:00 (KST) starting from December 5, 2016 till December 23, 2016 on Naver TV Cast (South Korea), YG Entertainment's YouTube Channel (International) and Miaopai (China).

source: Piotr Lisiecki
text: Piotr Lisiecki Piotr Lisiecki (born 2 March 1993) is a Polish singer and guitarist who rose to fame after placing third on the third series of "Poland's Got Talent". In late 2010, he was signed to EMI Music Poland. His debut album, "Rules Changed Up" was released on 27 April 2011. One week later, it placed eighth in Polish official sales chart.

source: Necrolust
text: Necrolust Necrolust is a demo album by the death metal band Vader released in 1989. The cover of the album was designed by Piotr Wiwczarek. Fenriz of Darkthrone cites this demo along with Celtic Frost's "Morbid Tales" and Bathory's "Under the Sign of the Black Mark" as key riff inspirations for "Panzerfaust".

source: Go to Hell (EP)
text: Go to Hell (EP) Go to Hell is a 7" EP by Polish death metal band Vader, containing two tracks from "Tibi Et Igni". The song "Where Angels Weep" was also released digitally. Both were released on April 18, 2014, through Nuclear Blast. There is a slight difference in mixing between "Go to Hell" and "Tibi Et Igni": the second guitar solo in "Where Angels Weep" was performed by Marek "Spider" Pająk, while on the album all guitars were performed by Piotr "Peter" Wiwczarek.

source: We Broke Up
text: We Broke Up We Broke Up () is a South Korean web series based on the webtoon of the same name, starring Sandara Park and Kang Seung-yoon (both from YG Entertainment).

source: Vader (band)
text: Vader (band) Vader is a Polish death metal band from Olsztyn. Formed in 1983, the group was founded by then-bassist Piotr "Peter" Wiwczarek and guitarist Zbigniew "Vika" Wróblewski. Vader went through several lineup changes over the years, with Wiwczarek as the only constant member. Since 2011, the band has comprised Wiwczarek on guitars and vocals, guitarist Marek "Spider" Pająk, bassist Tomasz "Hal" Halicki, and British drummer James Stewart.

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Answer: Piotr Wiwczarek