Spock is the product of a certain time, place, and upbringing. But what if the circumstances around him changed? The Star Trek universe offers viewers opportunities to view Spock in multiple dimensions. Here we observe Spock in the mirror universe, in the alternate time line, and in non-canon works.
Mirror Universe. Our first glimpse at "another Spock" is in the episode Mirror, Mirror, wherein a transporter accident sends Kirk, McCoy, Scotty, and Uhura to a mirror universe. While some things appear the same to them, others are reversed: the Federation is now the Terran Empire, the I.S.S. Enterprise crew sadistic and underhanded. Most remarkable of all, Spock - with a beard - may be the most coldly ruthless of all. Logic and rationalism, being morally neutral principles, still guide our Vulcan, but to personal rather than altrustic ends. He has no qualms about using the "agonizer" to discipline the men, and keeps personal guards on hand to protect his position. He is sullen and jaded, a contrast to our usual bright and eager Spock.
Yet there are hints from the beginning that Spock is different from his fellow crewmen. While officers advance in rank through assassination, Spock has no interest in assuming the captaincy. He is the only one to see past the bluffs of the displaced Kirk. Most significantly, he is open to change. A forced mind meld with Dr. McCoy reveals a different world to Spock, and Kirk uses this new understanding to engage the Vulcan. Spock clearly realizes the importance of restoring the officers to their proper universe, but Kirk convinces him that he must change his own by stating that it's illogical to support an unsustainable organization. It is implied that Spock takes command of the I.S.S. Enterprise and plants the seeds of change.
It's intriguing to consider how Vulcans fit into the mirror universe. If Spock remains a product of Vulcan upbringing, and Vulcan a member of the Empire, their society cannot be based on peace. Spock's past in the mirror universe will be revealed in an upcoming novel, The Sorrows of Empire by David Mack. The character is also part of a sequence of novels by William Shatner and Judith and Garfield Reeves-Stevens, beginning with Spectre.
Alternate Time Line. 2009's Star Trek film seemingly presents regular ol' Spock, distinct only from the Vulcan we remember because he is played by a new, young actor, Zachary Quinto. While he is the clean-shaven, reserved yet deep-feeling Spock we recall, his life is altered when a foe from Spock's future returns to the past. When the villainous Romulan Nero destroys Kirk's father's ship, the U.S.S. Kelvin, history takes a different course than the events in The Original Series and the films and shows that follow. This is the alternate time line, setting of new Star Trek stories.
Spock in 2009's Star Trek encounters some familiar problems, being a child of two worlds and fitting in to neither. He is bullied as a child (as we see in the animated episode Yesteryear), and chooses Starfleet Academy over the Vulcan Science Academy, to the chagrin of the Vulcan elders. (Though not to his father's deep disappointment, apparently.) He flourishes in this environment, designing a challenging test for cadets, the Kobiyashi Maru. James T. Kirk is the only one to defeat the no-win scenario, bringing him to Spock's attention.
While, inevidably, Kirk and Spock become friends (after a few equally inevitable stand-offs), Spock experiences several things in the alternate time line that he hasn't before: the destruction of Vulcan, the death of his mother, and a sustained romantic relationship.
Spock, in command of the Enterprise after Captain Pike is kidnapped, is too late in realizing that Nero has created a black hole to envelop Vulcan - for the sole purpose of watching Spock suffer. Vulcan is indeed destroyed, but Spock manages to rescue his father Sarek and the Vulcan elders, who, eventually, will restore their culture. Amanda, Spock's mother, is not so fortunate.
Spock represses the pain these events bring him. One imagines this causes incredible strain, since in TOS, he struggled to overcome emotions harboured since childhood - a lighter burden. We only see flashes of rage in TOS and the previous films; here Spock is overcome by burning anger. Fortunately, he doesn't have to handle it alone.
Uhura has apparently been Spock's girl for some time, and she consoles him after his terrible loss. Their relationship blindsides Kirk, and shows us that Spock has the capacity for tender feelings. In The Original Series, Spock's relationships never outlast an episode, and are fraught with tension. Still, Uhura is a logical choice for Spock since she is both level-headed and sensitive.
Sarek and Kirk provide further release, Sarek through wise words and Kirk through fisticuffs. We know Spock emerges from his despair with the strength to defeat Nero and face the future challenges to come his way. His make-up is different from the Spock viewers have long known, but the same principles - and friends - guide him.
Non-Canon. Star Trek's canon is comprised of everything we see on screen. (TV shows and films, with the exception of The Animated Series.) All other stories - novels, comics, video games, and role-playing games - are non-canon, not fitting into the events protrayed on screen, but simply using the same characters and setting. As such, there is much contradictory in non-canon works. While some fans wish the "expanded universe" were more coherent, the jumble allows for thousands of worthwhile stories to happen simultaneously.
Spock shifts and slides through nearly all non-canon TOS works, described in novels and drawn in comics and controlled in games. Due to the character's on screen consistency, it's fairly easy for good writers to portray Spock convincingly. Some authors, however, take Spock in new and unexpected directions, giving him back stories and "what if?" scenarios. Some of the best back stories are Vulcan's Glory by D.C. Fontana, and Spock's World by Diane Duane. Both novels go beyond describing Spock's actions, and delve into his mind and motivations. Other novels push Spock into the unfamiliar: Yesterday's Son by A.C. Crispin gives Spock a son by Zarabeth, while Vulcan's Heart by Josepha Sherman and Susan Shwartz goes further with Spock's romance of the Romulan commander in The Enterprise Incident. In Ishmael by Barbara Hamley, Spock even wakes up in 1860s Seattle!
As Spock tells his younger self in 2009's Star Trek film, "you can be in two places at once." Through the non-canon universe (and not to mention, fan fiction), Spock can be in many different times and places, each revealing new dimensions of his character.