Over the 10 seasons and two feature-length specials of Stargate: SG-1 the SG-1 team underwent more than one transformation. The original line up of Jack O’Neill, Samantha Carter, Daniel Jackson, and Teal’C is the most consistent team, with the brief addition of Jonas Quinn. Later, in season 9 and 10, Jack O’Neil was replaced by Cameron Mitchell and Sam Carter by Vala Mal Doran, creating a new dynamic.
Despite the team changes one thing remained consistent, the threat from several hostile alien races. From the Goa’uld through to the Ori, SG-1 has faced some incredibly complex threats. While some villains were short lived, others took much longer to defeat.
So who were the deadliest villains SG-1 ever faced?
10 Goa’uld System Lord Apophis
Apophis is the original villain of Stargate: SG-1. He gained power after Ra’s death (in the Stargate movie) and appears in the very first episode. After his then First-Prime Teal’C turns against him to join up with O’Neill, Apophis begins to mount his forces against Earth.
His System Lord persona is based on the Egyptian deity Apep, who embodies chaos. This is reflected in his actions as he seeks to take control of as many planets as possible.
Apophis is one of the longest surviving System Lords, appearing in 21 episodes in total. Most of these are in the first 5 seasons but he also recurs in alternative universes in later seasons.
9 The Replicators
The replicators are an invasive mechanical life-form who consume technology in order to duplicate themselves. They are hostile towards all other races but post a particular threat to the Asgard, allies of SG-1.
Later series show that they are controlled by a human form replicator known as Reese. She sees them as her toys and seems unable to comprehend how destructive they are.
They are resistant to energy weapons, but can be destroyed by projectiles weapons, such as SG-1’s guns. After O’Neill gained the knowledge of the ancients he was able to produce an ancient weapon which disrupted the cohesion between the Replicators blocks, finally defeating them.
8 Goa’uld System Lord Anubis
Anubis is a half-ascended Goa’uld System Lord, based on the Egyptian god of the afterlife with the same name. He rises to power after Apophis’ death and becomes a formidable enemy. After leading a huge assault on Earth, Anubis is defeated, almost. He survives the attack as energy but must restore himself.
He begins to rebuild his power in later series and build his army. His master plan is to destroy all life in the galaxy before repopulating it to his own design. He is eventually defeated by Oma Desala, who locks him in an eternal battle.
7 Replicator: Fifth
Fifth is a human-form Replicator who appears in Season 6. He lacks the programming issues encountered by Reese, the original human form on which he was based. This makes him seem more human and more dangerous.
SG-1 initially leave him in a time dilation field, which he later escapes. He finally meets his end when he is betrayed by the Replicator version of Samantha Carter which he created to rule with him. Patrick Currie, who plays Fifth, believes him to be misunderstood, rather than a villain.
6 Goa’uld System Lord Ba’al
Ba’al is the longest-running villain in Stargate’s history. He gains substantial power after Anubis’ defeat and begins a war against the other System Lords. He goes quiet and then reappears several times over the show's lifespan.
After Anubis’ return forces him to back down he collaborates with SG-1 to thwart Anubis. He then takes refuge on Earth, where he amasses his clones to try and take down the Ori. He is willing to do whatever it takes to gain power over others. It takes until Stargate: Continuum for the last Ba’al clone to be taken down.
5 Adria The Orisi
Adria is the daughter of Vala Mal Doran. Vala was impregnated by the Ori against her will by the Ori; leading to her carrying Adria, a genetically advanced human infused with Ori knowledge, known as the Orisi.
She is the Earthly leader of the Ori, ascended beings who use their knowledge to try and force other races to worship them. They were originally Ancients but they took a darker path, forcing others to obey their wishes and orders. Adria oversees the Priors, as they seek to spread the Ori's message.
4 Goa’uld System Lord Nirrti
When we first hear of Nirrti we discover that she has wiped out the entire population of the planet Hanka. The only survivor is Cassandra, a little girl who has been modified to be a living bomb, left as a trap for SG-1. Fortunately, Cassandra survives the ordeal.
Nirrti is focused on engineering an advanced human host for herself. After a run in with SG-1 she establishes a new base where she uses an Ancient DNA resequencer on the local population. This eventually becomes her downfall when the people she has experimented on turn against her.
3 The Priors
The Priors are the Ori’s presence across the planets. These humans have been artificially evolved by the Ori to be partially ascended, giving them god-like powers. The Ori then command the Priors to spread out across the planets, amassing followers.
The Priors gain followers at any cost, sending down plagues and other disasters to people who will not follow the Ori. They are essentially leaders of a giant cult, manipulating anyone in their path to bring power to the Ori.
2 The Lucian Alliance
The Lucian Alliance are a band of smugglers and mercenaries who have obtained Gao’uld technology and are trying to use it to gain power. As the System Lords have begun to fall at the hands of SG-1, the Lucian Alliance attempt to step up into the power vacuum created by their absence.
SG-1 come onto their radar after Vala crosses them, putting her and Daniel onto their wanted list. They remain as a background threat throughout later series before reappearing in Stargate Universe.
1 The NID
The NID proves that the biggest threats don’t always come from other planets. They are a team from Earth with ambiguous morals and loyalties. Using the second Stargate, discovered in Antarctica, they set about trying to procure alien artifacts for nefarious purposes.
Maybourne, one of the prominent figures in the organization, even tires to remove Teal’C in order to study him.
They manage to upset peaceful alien races, including almost causing the extinction of the Madronans. They also manage to attract a large amount of unwanted attention before they are eventually shut down.