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Julian Glover looks like he's having a whale of a time playing the campy pantomime villain. Of course, his casting only adds to my growing "GL copied Doctor Who" conspiracy theory LOL. He must have filmed this mere weeks after appearing in ESB but this wasn't Julian's first appearance in the Whoniverse. What's more notable, is that the character he plays is essentially the same as the one he would later play in 'The Last Crusade'. A similar profession in antiquities, the same self-satisfied attitude and even a similar taste in fine cut suits. Of course in TLC the big reveal is that he's secretly a Nazi but in this he's secretly a cycloptic green-tentacle-faced alien. And the Jagaroth spaceship...
...reminded me of something else JL later had a hand in (btw it takes off in the same way as the Federation Starships from that same sequence).
More SW tie-ins to come...
Kind of off topic, but I always thought Julian Glover's turn as Donovan was more directly inspired by his role in For Your Eyes Only (in both cases he plays the wealthy villain, who is initially presented to the audience as an ally of the main character, only to betray him later).
Spielberg probably was the one who cast Glover, since he seems to have always seen Indiana Jones through the prism of James Bond. After all, Lucas first coaxed him to direct Raiders right after Albert Broccoli refused to let him do a Bond film. (This also explains Sean Connery--apparently Lucas would have preferred Gregory Peck as Henry.)
OTOH, Jon Pertwee was another name tossed around for Henry, and I suspect he was Spielberg's backup choice. So Doctor Who may be in the list of influences on Donovan after all. But, given the Third Doctor's style, this brings us right back to James Bond.