Tacitus was

Preceded by Aurelianus (Aurelian)

Succeeded by Florianus (Florian)

Marcus Claudius Tacitus, as emperor: Marcus Claudius Tacitus Pius Felix Invictus Augustus. Extremely little is known about this emperor of 275-276. The Historia Augusta paints Tacitus as being mild and contemplative, no doubt inferring this from his numismatic portraits. However, the account of Tacitus in the Historia Augusta appears to be almost completely fictional. It seems relatively certain, however, as stated in the HA, that after Aurelian's murder, Tacitus captured and executed his murderers, and then successfully dealt with the barbarian invasions (Heruli and Maeotidae) resulting directly from Aurelian's death. These tribes were originally allied with Aurelian and were to join Rome in an attack on Parthia. Denied of this opportunity when Aurelian died, they turned on Rome instead, and were defeated by Tacitus.

The circumstances of Tacitus's death are uncertain. The HA says he was either murdered or died of disease, but Zosimus reports that he was murdered. HA also states that Tacitus was half brother of Florian, his successor, although no other ancient source mentions this.

"SPES PVBLICA" is probably the most common motto on coins of Tacitus. "CLEMENTIA TEMP[ORUM]" (as shown below) is also common. As noted by Robin Mc Mahon, Tacitus never used the title, deus et dominus natus (god and born ruler, or ruler of the world by birth right) as did his contemporaries, Aurelian and Probus, nor do any of his coins show Sol Invictus.

For a well-researched account of Tacitus, see Robin Mc Mahon's summary at De Imperatoribus Romanis - Tacitus.

For other coins of Tacitus, see the online reference at Wildwinds.com

Coin portraits (private collection):          

Tacitus AE Antoninianus (3.71g. 22mm). RIC 82C. Cohen 8. Ex Den of Antiquity, ex old collection.
IMP C M CL TACITVS AVG, radiate cuirassed bust right /
AEQVITAS AVG, Aequitas standing left, holding scales & cornucopia. 
 

Tacitus AE Antoninianus Antioch mint (4.32 g, 22 mm). Ex WCNC Online.
. RIC 210. Sear 3303. Cohen 20.
 IMP.C.M.CL.TACITVS AVG, radiate cuirassed bust right /
CLEMENTIA TEMP, Tacitus standing right receiving globe from Jupiter. "A" in field center. XXI in exergue
Uncirculated.