Vulcan (Gabriel Summers) is a fictional character appearing in American comic books published by Marvel Comics. He first appeared in X-Men: Deadly Genesis #1 (January 2006). He is the third Summers brother to be revealed, the younger brother of X-Men characters Cyclops and Havok.

Though a third Summers brother was mentioned years before by Sinister during an encounter with Cyclops, Vulcan first appeared in X-Men: Deadly Genesis #1, a story written by Ed Brubaker that ran from January to July 2006. Vulcan then appeared in "The Rise and Fall of the Shi'ar Empire" storyline, also written by Brubaker, in The Uncanny X-Men issues #475 to 486 (September 2006 to July 2007).

After Brubaker left The Uncanny X-Men, Christopher Yost took over as writer beginning with the X-Men: Emperor Vulcan mini-series, which ran from November 2007 to March 2008.

In July, 2008, Marvel.com posted a news article of an alternate cover of Emperor Vulcan featuring the phrase "Who Will Rule?", accompanied by the text "Stay tuned to Marvel.com and get ready for the blockbuster answer at San Diego Comic-Con!". This was all to build up to the "War of Kings" storyline, and Vulcan's part of the story is set up in the Kingbreaker mini-series, written by Yost.

Vulcan is the unborn child of Christopher Summers (later known as Corsair) and Katherine Summers, parents of Cyclops and Havok. After the Shi'ar kill Katherine, they take Gabriel from her body and place him in an incubator so he can fully mature.

While being sent to Earth to serve Erik the Red, Gabriel escapes and is found by Moira MacTaggert, who adopts him and helps him master his powers. Subsequently, he joins Petra, Darwin, and Sway in a mission to rescue the original X-Men from the sentient island Krakoa. However, Petra and Sway are killed by Krakoa, and Darwin and Vulcan enter stasis after transforming into energy and merging.

Reawakened in modern times by the mutant energy released during M-Day, Vulcan returns to Earth to seek revenge against Charles Xavier, killing Banshee in the process and kidnapping Rachel Summers and Cyclops.

Vulcan subconsciously uses the absorbed powers of Petra and Sway to manipulate the X-Men, and figures out the truth of the mystery behind the missing team of X-Men that were lost on Krakoa. Vulcan is able to lure Professor Xavier out of hiding, and confronts him in front of the X-Men, wanting the Professor to reveal to them all what really happened to Vulcan and his team. However, Xavier is unable to do so, because, in the wake of M-Day, he is no longer a Mutant. Enraged, Vulcan commands Marvel Girl to link their minds so that everyone can see what transpired. Reluctantly, Rachel does so, and with Xavier as a guide, she is able to not only reveal the truth behind what really happened on Krakoa, but she also detects another consciousness within the mind of Vulcan.