Has any Rebel defected to the Empire?

Question

I am wondering if there are any known persons that defected from the Rebellion to the Empire. There seem to be quite some defections to the Rebellion (for examples, see here), but nowhere have I found anything on defections the other way around or even double agents from the Empire.

Maybe the Rebellion was just a very nice place to hang out, but I can imagine there would always be those that regretted joining/being in the Alliance; maybe because they did not see a bright future for the rebellion anymore, maybe because they they did not approve of civilian casualties during missions (I don't even know if this was the case), maybe they just did not like the climate on Hoth.

Now I can imagine that the Empire would not be very forgiving towards rebel defectors, and the prospect of being 'questioned' for information, followed by execution, would probably not appeal to any rebel in doubt. Still, there might have been those that somehow (believed they) negotiated a favorable outcome for their future, in exchange for whatever information about the Rebellion they might possess, that could help the Empire.

Answer 1

In the game Rogue Squadron 3: Rebel Strike a Red Squadron pilot named "Sarkli" nephew of Admiral Piett defects to the Empire over perceived lack of respect for his abilities and achievements.

He joins the Empire as a spy and becomes a recurring antagonist throughout the campaign until killed by Han Solo while trying to stop him from escaping the exploding bunker on the sanctuary moon of Endor.

An Imperial officer in the Death Star hangar bay in Return of the Jedi is also identified as Sarkli making him a dubiously canon character.

Answer 2

In the canon comic mini-series Han Solo, the Rebel agent

Bot is revealed to be a double agent, apparently having been compromised and brain-washed into turning on his fellow agents by the Empire.

We see another less ambiguous traitor in Hill Purpura, from Bounty Hunters.

Tal Hezs from the Legends series Empire is another example.

Answer 3

There are at least two examples in the X-Wing series of characters who were Imperial double agents who pretended loyalty to the rebellion, namely

Erisi Dlarit and Gara Petothel

and one who wasn't loyal to the Imperials, but was willing to betray the Republic for a bag of cash

Galey, the cook on Mon Remonda

and a disquieting number of people in that series got brainwashed to various extents.

However, I know of no case where someone unambiguously betrayed the Rebel Alliance or New Republic on ideological grounds, having previously sincerely believed in its cause.